In order to improve the dynamic range of CMOS image sensor and apply it to day night compatible imaging, a new dynamic range expansion method is proposed in this paper. In this method, multiple reset barriers are set in the pixel to prolong the saturation time of photodiode in the exposure process. At the same time, by switching the pixel integral capacitance in different imaging environments, the response sensitivity of low light level imaging and the full well capacity of high light level imaging are improved, so as to realize day night compatible high dynamic imaging. MATLAB simulation shows that this method can expand the dynamic range of traditional CMOS image sensor from 61dB to 102dB.