In this paper, characteristics of phase modulation of ZLI-1565 nematic liquid crystal is studied, The resulut indicate that parallel aligned LC has larger phase shift amount and less changes in amplitude. Based on the study, a new phase-shifting shearing ESPI system which use parallel-aligned liquid crystal as a phase modlator is set up. This method increases the mearsuring accuracy of shearing ESPI by combine phase-shifting technology with shearing ESPI