The inventive concept relates to a CMOS image sensor and an operating method of the CMOS image sensor. The operating method according to an embodiment of the inventive concept includes generating photoelectrons at a photo sensor element during a first time; generating photoelectrons at the photo sensor element during a second time shorter than the first time; and sensing the photoelectrons generated at the photo sensor element. A gate voltage of a transfer transistor connected to the photo sensor element is set differently at the first time and the second time. With an embodiment of the inventive concept, a dynamic range of the CMOS image sensor increases.