With the development of the testing verification of the equipment system, there are a huge number of fault samples, long test cycle and high cost in the radar transmitter system. A method based on improving the information entropy and Bayes posterior risk criterion is proposed to optimize the fault sample size. Based on the virtual test data of radar transmitter subsystem, using the method of improving information entropy, obtain the system-level test data by converting the system subsystem, and then determine the total test samples and the maximum number of failures, which determine the test scheme. Taking the fault detection rate of the radar transmitter system, the test fault sample size of the proposed method is 165, reducing the fault sample size by 64.97% and 51.18% compared with the classical sampling and sequential probability ratio test methods, respectively, verifying the effectiveness of the proposed method to some extent.