To improve the efficiency of phase modulator,the ring resonator which is equivalent to Maher-Zehnd′s upper and lower arm was proposed by combining the advantages of the optical microring and Mach-Zehnder.The normalized output intensity and output phase were derived by coupled-mode theory.The effects of the transmission loss factor and the coupling angle on the normalized optical intensity and phase were numerically analyzed.The analysis results show that the output light spectrum cyclical changes as phase-sensitive ring phase changes.When the coupling angle increases,the output light spectrum becomes more acute,the output of π need the greater phase modulation.When the transmission factor is small,the phase change is relatively flat spectrum,the difference between maximum and minimum values is not met π.By optimizing structure parameters of Mach-Zehnder microring resonator,sensitive ring structure can improve the modulation efficiency.Simulation results show that when the phase shift of the sensitive ring is 0.1π,the output phase shift can be achieved π,and the normalized intensity can be kept 0.9 at the same time.The consistent requirements of phase shift and signal amplitude in differential phase shift keying is implemented,which providing a theoretical basis for further study of phase modulator.