In mechanical installation, it is almost impossible to install the zero point of sine and cosine encoder as the zero point of UVW three-phase permanent magnet us motor. In order to obtain synchronous control, it is necessary to find the difference of zero signal to compensate before the drive control operation. In the software design, the function of magnetic phase angle self-learning is set up in the design of Xiwei inverter. The deviation of phase angle can be found before the operation and start-up, and the synchronous control effect is obtained.