Abstract: Two methods of microwave phase measurement and its applications in theresearch and operating of microwave accelerating system for BEPC Linac aredescribed. These applications are as follows: measurements of phase noise,modulation, jitter and drift, the phase sensibility on voltage of the klystron andTWT amplifiers, the temperature monitor and the selection of optimum operatingtemperature for accelerator sections, the phasiug system etc.