TDM MIMO configuration widely used in high-resolution imaging radar system has several performance problems due to Doppler ambiguity. In particular, Doppler ambiguity degrades DOA estimation accuracy, making it difficult to detect an object position and utilize it. In this paper, we propose a new method to minimize the effect of Doppler ambiguity on DOA estimation rather than improving DOA estimation accuracy through accurate estimation of Doppler ambiguity. In order to suppress the phase error due to motion, Non-Coherent Integration (NCI) and Integral Phase Error Alignment (IPEA) methods are devised and experimentally verified by evaluating the DOA estimation accuracy for a moving target.