Abstract: The paper briefly analyzed the principle of flux observation of synchronous motor based on voltage model. In order to solve problems of DC bias error and zero-drift caused by integral link in traditional voltage model, it proposed a model of flux observation based on voltage model in MT coordinate, and put forward integral negative feedback in the model. The simulation result showed that compared with flux observation based on traditional voltage model, the one based on voltage model in MT coordinate has better stability and can restrain DC bias disturbance and integral zero-drift.