We can't know. you have not provided any exact comp settings, render settings, system info, details about your footage, what version of AE, how you verify the rendered file. Pardon me, but this is simply completely useless.
ok, both Flash and After effect are CS6, i have a Lenovo Ideapad, can handle 64 bits
first i exported the video on .MOV from Flash CS6, without any problems
Then i finished the edition on After Effects, everything look good.
i have tried to render it on MOV, AVI, MP4 and the audio for the video that was exported from flash always get out of sync. i dont really move anything else
There's probably something to do with frame rates, bit rates or something similar. What are the exact specs of the audio file? How many kHz, etc.?
What are your render settings?
For what it's worth, I don't use AE to do anything with audio. I either use proper audio software like Audition or, if I'm putting it to video, I use a video editing program like Premiere Pro.