An efficiencyoptimizing control method for direct torque controlled interior permanent magnet synchronous motor (IPMSM) was proposed. Based on the model of IPMSM taking into account iron losses, the dependences of power losses on the output torque, speed and stator flux were analyzed in detail. According to the characteristics of the classical direct torque control which did not use the zero voltage space vectors, the expression of the power losses could be simplified. The stator flux linkages which achieved the maximum efficiency were obtained in the different operating conditions. The simulation results showed that the proposed control method not only preserved the fast torque dynamic response of the direct torque controlled driving system, but also improved the efficiency of the motor in steady state operation.