I uploaded an app built with 1.5 SDK into market, but someone told me they can not find it in the market in their phone. I do not know why, because I have test it in 2.1 emulator.
Then how to know if my app is available in android market with all versions, is there any url to test that?
There are a couple of Web front-ends available to the market where you can check if the app appears in principle. E.g. http://www.cyrket.com
Whether the market lists your app from a specific phone depends on the phone and the resources your app needs. E.g. if your app does not support small screens (you can set this in the manifest), the market won't list it for phones like the HTC Tattoo.
Apparently the sequence in which apps are displayed by the market also varies by phone, carrier and country. You can get the app "Market Enabler" which allows you to make your phone pretend it's in a different country, in order to check if your app displays fine for all country markets.