如果您使用的是 Mac OS 10.7.x 并且已经升级到 Xcode 4.6，那么您可以拥有或下载模拟器 4.3 版本.但是，如果你使用的是 Mac OS 10.8.x，那么你不能有模拟器 4.3 版本.原因是 Mac OS 10.8.x 上的 4.3 模拟器崩溃了很多，因此 Apple 已将其删除.

查看此链接:-
http://iphonedevsdk.com/forum/iphone-sdk-development/111568-what-happened-to-the-ios-4-3-simulator-in-xcode-4-6.html

If you are using Mac OS 10.7.x and have upgraded to Xcode 4.6, then you could have or download simulator 4.3 version. But, if you are using Mac OS 10.8.x, then you can not have simulator 4.3 version. The reason is 4.3 simulator on Mac OS 10.8.x crashed a lot, so Apple has removed that.

Check this link:-
http://iphonedevsdk.com/forum/iphone-sdk-development/111568-what-happened-to-the-ios-4-3-simulator-in-xcode-4-6.html