The transmitting waveform distortion was happened during a system test of a batch of T/R module.Through analyzing the fault cause,it has been found that there exist tree aspects of problem.First,the attenuation manager types and the attenuation volumes of the T/R module test system and the complete machine were different,thus resulted in the test results inconsistency.In addition,the related test of T/R module was only applied a standard excitation according to the technology agreement requirements and no static test,thus the small signals input resulted in the self excitation.Third,the necessary precautionary measures to avoid overshoot was failed when the amplifier of T/R module was supplied in a pulse power way.