Based on rotor field oriented vector control system for permanent magnet synchronous motors (PMSM), rotor harmonic flux and motor parameters and the way they affect current controller performance were analyzed. The coupled voltages deteriorated current controller performance in high speed. This was because the field current component and torque current component could not be decoupled completely in rotor field oriented vector control. According to series decoupling theory, a deviation decoupling method was proposed. The feedback decoupling control and the proposed deviation decoupling control were contrastive analyzed. Simulation and experimental results showed that the deviation decoupling algorithm was robust against parameter changes, and could suppress harmonic disturbances. It had a good decoupling ability in high speed.