Accurate measurement of current feedback is an important prerequisite for high performance permanent magnet synchronous motor (PMSM) drive system.For the actual control system,due to the thermal drift,aging,nonlinearity and some other factors of the current sensors and the corresponding conditioning circuits,current measurement error will occur,more specifically,the current measurement offset error will result in torque and speed ripple whose frequency is one time of electric frequency,and this may deteriorate the PMSM control performance.On the basis of analyzing the influence of current measurement offset error,the influence of closed-loop control to the current ripple amplitude was studied,and it was pointed out that the traditional deduction could not stand when the influence of closed-loop was considered.Aiming at this issue,an online current measurement offset error compensation for PMSM drive system based on discrete Fourier transform was proposed.In the proposed method,the current ripple was extracted and the current measurement offset error was compensated during the motor operation in order to suppress the torque and speed ripple caused by current measurement error.Compared with the traditional methods,the proposed scheme did not need the information of motor shaft inertia or stator resistance.Finally,the effectiveness of the proposed algorithm is verified through PMSM used in CNC machine tools.