An analytical model of modulation transfer function (MTF) for time-delay-integration (TDI) CMOS image sensor with oversample-superposition in the scanning direction is proposed. Impacts of sample number in a line-time, superposition number, TDI stage and velocity mismatch ratio on scanning MTF are studied based on the along-track-rolling exposure readout principle. To verify the scanning MTF model, an imaging simulation system is established, which is based on analysis of geometric and energy transmission relationship from continuous scene to discrete image on the TDI-CMOS image sensor. Then knife-edge method is used to calculate the MTF curve. The simulation results show that scanning MTF increases with the increase of sample number, scanning MTF is negatively related to superposition number when sample number is fixed, and scanning MTF decreases with the increase of velocity mismatch ratio and number of TDI stages.