To address the speed limit of Interior Permanent Magnet Synchronous Motors（IPMSM） due to DC bus voltage, a simplified flux-weakening control method based on voltage coordinate system was presented. The analysis of vector control based on current coordinate system is converted into voltage coordinate system, and the expression of torque based on voltage coordinate is derived. With weakening control strategy, the current components are controlled according to the limit voltage. Theoretical analysis and simulation results have shown that this method has such advantages as simple calculation, maximum efficiency of DC voltage, wider range of speed and good dynamic response.