I have just have my app approved in the App Store, but only devices running 4.0 can download it. The project settings in Xcode says "base SDK 4.0" and the "deployment target 3.1.3".
Is there some other setting or value in my plist file or thing I have set in iTunes connect that could yield such a result.
I use no 4.0-only API's and would like people running 3.1.3 and up to be able to use the app.
There is a bug in XCode that I think may be the reason for your problem: You need to do all the project settings BOTH for the current target (select target and hit cmd + i) and in the project settings (project > edit project settings). The two forms are absolutely identical and hold the same information, however they do not correspond to each other - changes made in one form wouldn't reflect in the other. So, make sure to fill in the necessary information in both places and also make sure you're using the same configuration (debug, release,..) for each form.
edit: I'm not quite sure if this is really a bug or rather a feature - it caused me some trouble however because of similar problems with producing builds for ad hoc distribution.
来源：https://stackoverflow.com/questions/3559936/app-store-say-requires-ios-4-0-but-deployment-target-is-3-1-3