The disclosure discloses a CMOS image sensor, which includes a plurality of image sensor units and a resistance-to-digital converting unit. Each image sensor unit includes a pixel unit and a resistive random access memory unit connected to the pixel unit, the pixel unit is configured to convert a received optical signal into an analog signal and the resistive random access memory unit is configured to convert the analog electrical signal into a resistance value. The resistance-to-digital converting unit is connected to the plurality of the image sensor units, and is configured to convert the resistance value into a digital signal. The resistive random access memory unit is adopted in the present disclosure to replace a transistor device and is configured to convert resistance information of the resistive random access memory unit into a digital signal and output. Thus, digital quantization of image information is completed.