An approach to optimize the aerospace software test cases based on the requirement coverage is researched in this paper to improve the efficiency of the software testing and increase the effectiveness of aerospace software testing. It is composed of the reduction and design of test cases, and has been used in a test of aerospace project. Firstly,the characteristics, testing process, and optimization techniques of aerospace software are analyzed. Then, a method to reduce test requirements is improved to simplify the test requirements. Furthermore, a design of test cases based on the correlative keywords of requirements is given, and the requirement coverage is achieved. Finally, the optimizing approach is applied in the test of aerospace software. The results of application show that the method can not only satisfy the demand of requirement coverage, but also make the workload of designing test cases reduce by 39%. The method ensures testing adequacy, and improves the test efficiency greatly.