Abstract: Synchronous reconstruction technology has been used in High-resolution magnetograph of New Vacuum Solar Telescope, which uses the beam splitter. The beam splitter is designed to reduce the polarization effect, but still inevitably affects the polarization measurement of the solar magnetic field, therefore, the measurement of the polarization characteristics of the beam splitter is necessary for NVST's polarimeter. In this paper, Mueller matrix of air is used to calibrate the measured Mueller matrix result of samples, and two beam splitter samples are measured in this method. The Mueller matrix of different beam splitters and their influences on the polarization measurement are compared. The Mueller matrix of the flat glass is measured, which varies with the incident angle, and the deviation between the measured result and the theoretical value is compared. The accuracy of the Mueller matrix measurement system is 5×10^-3 after the air Mueller matrix has been used for calibration.