We proposed a method to measure the optical constants of thin film through polarizing phase shifting interferometer based on Twyman-Green interferometer structure. A broadband light source coming with a narrow band-pass filter was used to generate a low coherence light and the wavelength is tunable by changing the filter. A pixelated micro-polarizer mask on the detection camera made phase shifting array to make different phase shifts at once. Therefore, we can use one single interferogram to extract phase information, and it is effective in reducing environmental vibration. The refractive index and thickness of thin film can be derived from the obtained reflection coefficient's magnitude and phase. The measurement results were compared with the results obtained by an ellipsometer.