ing at systematic error sources in a Mueller matrix imaging polarimeter, we propose a simplified analytical method based on the approximate matching of the ideal coefficients of Fourier series of the intensity curve with the real ones. By using the method, a linear relationship between the deviation of the Mueller matrix and the parameter of the error source is built. The analytical expression for random error caused by the azimuthal angle is complex, so an equivalent noise model is proposed to characterize the impact of misalignment from the view of statistics. Based on the simplified models above, we conduct a comprehensive analysis for the measured Mueller matrices influenced by six kinds of systematic error sources and two kinds of random error sources. The simulation for the measurement of a typical Mueller pupil of the lithographic projector is performed. The results verify the accuracy of the proposed method.