In order to design an optimized test case to test web application, a method of equivalence partitioning is used in this paper. Based on the evaluation of equivalence classes for the input condition, the web application of the Accela GIS module is divided into seven partitions, and the twelve vital test cases are designed. The results of test show that the process of executing the test program can find errors, and in particular, the test cases have the high probability of finding as-yet-undiscovered errors. These test cases can basically cover all of the test points and be repeated less. The equivalence partitioning is effectively designed into test cases of the web application, which are feasible, strong and easy to be understood, to reduce the total number of test cases that must be developed.