A CMOS image sensor with coupling capacitor based AC-coupled CTIA and digital CDS was proposed. By adding a coupling capacitor to the conventional CTIA circuit, the dark current of the photodiode was reduced via controlling the bias voltage of the photodiode; Meanwhile, an off-chip digital CDS was adopted to reduce the reset noise of the pixel and the FPN by realizing the subtraction algorithm between the reset signal and pixel signal after A/D conversion off-chip. This CMOS image sensor was implemented in the 0.35 μm standard CMOS technology. The pixel array was 256×256, and the pixel size was 16 μm×16 μm. The experimental results show that the dark current can be minimized by reducing the bias of the photodiode nearby zero. The temporal noise and FPN are obviously reduced after adopting the off-chip digital CDS.