The spatially modulated imaging polarimeter is a compact, static and simultaneous polarization imaging system which can collect the interferometric data in real time. By processing the interferometric data, the complete polarization information of the incident light can be demodulated to realize the polarization detection. Based on the device principle of the spatially modulated imaging polarimeter using Savart Plates, the interference pattern processing method in the frequency domain was analyzed. Then, the physical mechanism of the modulation was explained and its corresponding processing method in the spatial domain was analyzed. Finally, in order to evaluate and compare the two methods, the simulation was performed and a prototype of the polarimeter was developed to finish the field experiment. The experimental results show that the spatial processing method can effectively extract the polarization information from the interference pattern. It can identify the artificial targets more clearly from the natural background compared with the frequency-domain processing method.