Abstract: Mach-Zehnder heterodyne interferometric polarimeter can precisely measure the polarization state of light in real time.In order to improve the measurement precision and reduce the nonlinear erzor,which arises from the elliptical polarization of the laser,polarization leakage of the polarized beam sputter(PBS) and misalignment of the PBS were analyzed.The erzor formula was deduced.The simulation results showed that different amplitude ratio and phase difference of the measured beam had different nonlinear error output.The erzor was quite similar to the nonlinear erzor calculated in the Michelson heterodyne interferometer.