Abstract: The traditional four-step phase shifting algorithm has some limitations (such as phase shift error, low resolution and coherent noise) for processing of phase-masked interferograms, which affects the performance of the dynamic phase-masked interferometer. In order to improve the analysis accuracy of the phase-masked interferogram, a phase demodulation method based on low-pass filtering is proposed. According to the fact that the phase introduced by phase mask has much higher spatial frequency than the measured phase, the proposed method extracts the phase from phase-masked interferograms by a low-pass filtering method. Numerical simulation shows that the proposed method has a higher accuracy than the traditional four-step phase shifting algorithm. The accuracy of the proposed method can be