Based on the mathematical model of the permanent magnet synchronous motor (PMSM) and the maximum torque per ampere (MTPA) control method, the mathematical properties of the MTPA curve were analyzed. The MTPA curve was the left half of the equilateral hyperbola. According to the characteristics of this hyperbola, a piecewise linear MTPA approximate control algorithm was proposed. The portability of this control algorithm was proved by changing parameters of the motor and calculating errors between true value and approximate value. A Simulink model was established for simulation analysis. The response properties of lookup table method and piecewise linear algorithm were compared. The simulation results showed that the piecewise linear MTPA approximate control algorithm had good steadystate and dynamic response, and could well realize the MTPA control method.