how to get the rate(top/ps) of cpu and the usage of memory?

Can i do that? or It's 开发者_如何转开发a private API?

No, there are not API's for this.

How to display iPhone free memory ? and how to free iPhone memory?

You can get the total memory usage of your app and total free memory in the system with the code posted in this other question.

Of course, free memory varies depending on what background processes are running at the time and what's in the autorelease pool(s) at the moment, but it does give you some idea.