Bistatic synthetic aperture radar refers to a SAR system that the transmitter and receivers are placed in different platform. Because Bistatic SAR effectively avoids many shortcomings of conventional SAR, it becomes the research hot spot in the world of late years. Thereamong ATI is an important working model. In our work, we first analyze and research the imaging model of ATI in Bistatic SAK then derive the velocity formula of the moving target. Next, we analyze the interferometric result in the case of arbitrary transmitter and receiver platforms. At last, we verify the accuracy of the formula by using the simulation and actual data, and declare the availability of the model. The result shows that the ATI technology can measure the radial velocity of the slowly moving target in Bistatic SAR system. If the direction of the baseline is arbitrary, by modifying the formula, we can get well result equally.