How Kaito Kid knew the true identity of Edogawa Conan (Shinichi Kudo)??

I personally think Kaito is almost as smart as Shinichi and is smart enough to figure out that a normal kid wouldn't always be able to figure his plans out and act like how Conan does (episode 76 is proof xD).

I'm not completely sure about how he knew he was Shinichi but he probably guessed that one of the only people to outsmart him would be Kudou Shinichi.

in the 3rd movie he listened to conans phonecall with dr.agasa and also conan is so smart for his age so he figured it out

In Movie 14, Kaito Kid heard the conversation between Conan and Professor Agasa about the childhood memories between Ran and him, so I guess that Kaito figured out that Conan actually is Shinichi Kudo since he is talking about his childhood friend, Ran when they were small kids but Conan now is indeed a kid.

Kaitou Kid (also known as Phantom Thief Kid) becomes aware of Conan's true identity in The Last Wizard of the Century. While disguised as Ninzaburo Shiratori, Kid had bugged the phones on the Suzuki Group's ship and therefore heard all of the conversation between Conan and Agasa on the phone. Not realizing they were being listened to, Agasa continued to refer to Conan as "Shinichi" on the phone as he normally does. It is assumed that afterwards Kid put two and two together. Kid's knowledge of Conan being Shinichi is confirmed in The Lost Ship in the Sky. Kid's knowledge of Conan's identity has not been stated in the manga and has not been confirmed by Gosho Aoyama to be canon, although in the manga Kid is definitely aware that Conan is no mere child.

Kaitou Kid (also known as Phantom Thief Kid) becomes aware of Conan's true identity in The Last Wizard of the Century. While disguised as Ninzaburo Shiratori, Kid had bugged the phones on the Suzuki Financial Group's ship and therefore heard all of the conversation between Conan and Agasa on the phone. Not realizing they were being listened to, Agasa continued to refer to Conan as "Shinichi" on the phone as he normally does. It is assumed that afterwards Kid put two and two together. Kid's knowledge of Conan being Shinichi is confirmed in The Lost Ship in the Sky. Kid's knowledge of Conan's identity has not been stated in the manga and has not been confirmed by Gosho Aoyama to be canon, although in the manga Kid is definitely aware that Conan is no mere child.

It is in Movie 3

yes.but kaitou dont sure yet...about conan identity....becaue.at movie 14.kaitou ask conan.where shinichi now........

Kaito kit masquered as Shiratori and heared Conan talks to Professer Agasa in movie 3.

Well I personally think that somewhere in the Phantom Thief Kid, Kaito Kuroba's father - the original Kid would have told him. Yusaku and Toichi were companion/competitor after all. It was actually Yusaku who gave Toichi the name 'Kaitou Kid' in the first place, so I guessed that Toichi would have told his son about the origin of their successive alias.
The second thing is that both of them are prodigies. It wouldn't be hard to figure out that it was the other who's behind all the failed plans/attempts at stealing some treasured jewels. You know what they say right? "Like father, like son". They are the exact replicas of their fathers in both appearance and brain alike. They might have inherited a few traits from their happy-go-lucky and overly 'loving' mothers which just make them both the more sarcastic when it comes to victims of childish behaviours.
Kuroba and Kudou are so alike in family background and intelligence that I wouldn't be surprised if it turns out that they were some kind of childhood best friends. Or even ended up helping each other with girl problems...which would probably be quiet disastrous since they're both total suckers at relationships (perhaps either Hattori or Hakuba can lend a helping hand).
Hope this answer helps. It's just my opinion on the issue. ^^

watch movie 14

WHEN CONAN AND RAN TAKE A BATH

I think when in movie 3 and 8

Kid heard the conversation between Conan and Agasa

Kaitou Kido-san knows the identity of Shinichi Kudou thanks to Episode 76, Conan vs Kaitou Kido. During the course of the special that introduced him, Kido ended up disguising as Ran and figuring it out over the course of the events; namely a showdown between the two of them.

Kaitou Kid knows that Conan is Shinichi only in movies and maybe OVAs. But in the anime Detective Conan Kaitou Kid is not aware that Conan is Shinichi but is aware that Conan is no ordinary kid..

In the "Detective Conan Super Digest Book", a journalist asked how the Kid knew Conan's real identity. Gosho answered that "well...he searched ! (laugh)".

Err~ but kid already knew his true identity (conan/shinichi) before.. it was on movie 3 when kid disguise as shinichi.

In episode 76, where kaito kid makes his first appearance, he might have heard the professor calling him shinichi. ;) Ps. Those who said movie 14 think about it how can kaito kid known that conan is shinichi a few movies after movie 3 (what the asker is asking)? Unless he travelled into the future.

on movie 3 ,,, kaito kid take a sheratori character and nobody know's that

It does show that in Movie 3 Kaitou Kid knows who Conan really is, but it's non-canon, and Aoyama Goshou hasn't confirmed that Kid knows Conan's identity yet. Well somehow he does seem suspicious about him being too intelligent for a child.

In movie 3,while disguised as Ninzaburo Shiratori,Kid had bugged the phones on the Suzuki Financial Group's ship and therefore heard

Kid discovered Conan's true identity in Movie 3. Kid overheard Conan talking on the phone as Shinichi when he was disguised as Shiratori. The movies aren't considered canon, however, so in the continuity of the manga and anime, it's assumed that he doesn't know.

In the 3rd movie 'The Last Wizard of The Century' kaito kid was disguised as sheratori.He followed conan, he heard him talk to professor agasa and saw find the puzzles solution etc.

In Movie 3,Kid eavesdrop Agasa and Conan's secret talk.That Kid why that son of a!!!!!!!!.

Well first of all Kaitou is not dumb as mouri. he must have added the facts that when conan came shinichi went and he is WAY TOO smart and all the stuff. To confirm it he disguised as shiratori in movie 3 and also heard what he said and was sure that he was shinichi. I hope this answers your questions!!