In order to improve the ranging accuracy of dual-channel gain modulation array three-dimensional imaging radar system, taking into account the compactness of the system structure and based on the working principle of TDI CCD which can make use of drive circuit to cumulative exposure information of multi-level of the same point, CCD replaced by TDI CCD as photo detector is presented. According to the ranging principle of this three-dimensional radar, ranging formula and ranging accuracy formula of imaging system are derived. The impact of the level of TDI CCD and the absolute error of velocity mismatch on range accuracy and the modulation transfer function (MTF) is studied. And the analyzing result shows that the accuracy of the distance can be improved to times of the original by this method, and the high precision motion compensation can be realized without additional motion compensation device.