The invention relates to an amplitude and phase stability testing method of a coaxial cable and belongs to the communication microwave signal measurement technical field. According to the amplitude and phase stability testing method of the invention, a multichannel amplitude and phase testing system is adopted to test the amplitude difference and phase difference of a coaxial cable to be measured and a reference coaxial cable, and the stability of the coaxial cable can be analyzed through comparing the amplitude differences and phase differences of the coaxial cable and the reference cable under various states, and therefore, the stability testing of the amplitude and phase of the coaxial cable can be completed.