Abstract: With approximation of little amplitude aberration modes, we present theoretical analysis and explore validate conditions of MBWFS. We also compare and analysis three ways of extracting information from intensity distribution in measurement plane and three definitions of sensor output signals, respectively. Performance difference of sensor to detect single and multiple modes is numerically studied in terms of Zernike aberration modes. The results show that, sensor sensitivity indicates aberration modes component and amplitude included in test wavefront, which are identical or relevant with those in bias-screen plate, but sensitivity to each Zernike aberration mode is different, and furthermore, irrelevant aberration modes can affect both output signals and sensitivity.