The invention provides a CMOS (Complementary Metal Oxide Semiconductor) image sensor which comprises a pixel unit, wherein the pixel unit comprises a reset transistor, a selecting transistor and an amplifying transistor; the reset transistor comprises a source electrode, and the source electrode is used as an inducing node of the pixel unit. The CMOS image sensor also comprises a reset unit, wherein the reset unit improves the potential of the inducing node to a high potential when an input first signal is the high potential and increases the channel resistance of the reset transistor when the first signal is converted into a low potential from the high potential. By increasing the conducting resistance of the reset transistor, the reset noise bandwidth is relatively reduced so that more reset noise can be removed by a negative feedback operation amplifier.