In the traditional software testing, a large collection of test cases of the tested system automatically generated, in the process of actual execution, all of the test cases are executed is not possible. Normally, we test a certain function of the tested system, so choosing the test cases about a certain function is very important. This paper focuses on solving the problem of choosing test cases about a certain function of the tested system based on CPN model, the method which is based on purpose is used in this process. In the process of test cases selection, there are a whole lot of repeated calculation and operation, this characteristic just can make it combined with the parallel advantage of cloud computing. In summary, this dissertation focus on the test cases selection problem, using MapReduce programming on Hadoop platform, a test case selection tool is designed to improve the efficiency and service capabilities of test selection, the result of the experiment is consistent with the expected result.