The sensitivity of CCD pushbroom scanning imaging system is analyzed systematically. The equations for system s NEΔρand MBΔρ are derived, and An exhaustive study of the system s MTF is made. Especially, from the scanning and operation characteristic of CCD, we differentiate the convolution and interval integration process on the Y-direction from the sampling process on the X-direction. And the integration MTF4 on the Y-direction is analyzed severely. The exact expression of MTF4 is obtained as follows