I've lost all my bought app in App Store.what can I do?

If they're not in iTunes on your computer so you can just resync them, go to the iTunes Store, log into your account, and click the Purchases link under the Quick Links. From there you should be able to re-download some or all of your apps or other purchased content. Note that not all media content has been licensed for re-downloading in all countries at this time.

For full instructions, see:

http://support.apple.com/kb/ht2519

Regards.

Forum Tip: Since you're new here, you've probably not discovered the Search feature available on every Communities page, but next time, it might save you time (and everyone else from having to answer the same question multiple times) if you search a couple of ways for a topic, both in the relevant forums and in the Apple Knowledge Base, before you post a question.

If an app is not showing in Purchased, then it's probable that you purchased that app using a different Apple ID.

But again, if the app is in iTunes on your computer - and by that I mean that you previously downloaded or synched the app to iTunes so it's currently in the iTunes library - then you can just resync it. to the iPhone. Otherwise you need to sign into the iTunes Store, on whatever device you choose to use, using the Apple ID through which you purchased the app.

Regards.