I want test my application in .net with testing software.what of them is reasonable?how can I choose?

I assume that your question is not regarding unit-testing tools but rather automated functional testing tools.

Before kicking off the test tool evaluation process, you should establish your compulsary and optional test requirements and determine your budget.

Your test tool evaluation process could have the following steps:

1) Create a list of tools available to you: Depending on your budget, you could either choose to explore only commercial tools or open source/ freeware tools or both. You can find links to a few popular commercial tools at http://en.wikipedia.org/wiki/List_of_GUI_testing_t...

You can find a list of 83 open source functional testing tools at http://www.opensourcetesting.org/functional.php

2) Explore each tool with regard to your requirements. The initial study of each tool could be done from the material available on the tool's website or with the available literature. Remove from your list the tools that do not satisfy your requirements.

3) Try out the short-listed tools to automate your tests: At this point, you might have only a handful of tools remaining in your list. For each tool:

a) Download a copy of the tool. Many commercial tools have limited-time evaluation copies available. You can, of course, download the complete open source tool.

b) Automate a couple of tests. Be on the lookout for any problems in automation e.g. inability to recognize objects, steep learning curve, recording/ playback problems etc.

By the end of this process, you should have a fairly good idea of a good tool to automate your tests.