Embodiments of the present invention provide a correlated double sampling (CDS) circuit and a CMOS image sensor unit using the CDS circuit. The CDS circuit shifts levels of sampled sensing signal and reset signal with equal amounts. Thus a voltage difference of the sampled sensing signal and the reset signal remains unchanged, and their levels may fall within a linear input range by adjusting their levels. Compared to a conventional CDS circuit, a gain of the CDS circuit provided by the embodiment of the present invention is not reduced, and thus a design complexity of a rear circuit thereof is lower, and an induced noise is relatively low. Furthermore, the CMOS image sensor unit using the CDS circuit provided by the embodiment also has these advantages.