1、打开eclipse
2、在自己创建的项目中找到res,点击打开，点击project.properties，看到# This file is automatically generated by Android Tools.# Do not modify this file -- YOUR CHANGES WILL BE ERASED!## This file must be checked in Version Control Systems.## To customize properties used by the Ant build system edit# "ant.properties", and override values to adapt the script to your# project structure.## To enable ProGuard to shrink and obfuscate your code, uncomment this (available properties: sdk.dir, user.home):#proguard.config=${sdk.dir}/tools/proguard/proguard-android.txt:proguard-project.txt# Project target.target=android-21
3、看到最下面一行的android-21了吗？修改这里就行了，当前21指的是android5.0版本，你可以修改数字成19或者其他，19是android4.4的
