The invention relates to the field of image sensors and discloses a metal oxide semi-conductor image sensor. According to the invention, the function of bimodule reading is realized through the structure of the metal oxide semi-conductor image sensor, the dynamic range of the image sensor can be expanded effectively, and both the circuit structure and the logic control are simpler. Through related double sampling, noise can be reduced effectively, and S / N ratio of readout signals can be improved greatly. Under the condition of stronger ambient light, reading is performed in a PPS (Passive Pixel Sensor) mode, and electric charge is read directly without magnification, so that the circumstance of saturation of C-APS (Active Pixel Sensor) due to excessively strong light can be avoided, however, under the condition of poor ambient light, reading is performed in a C-APS (Active Pixel Sensor) mode, and variable gain reading is realized through different offsets, therefore, the dynamic range of the metal oxide semi-conductor image sensor can be expanded greatly.