The back-stepping control method for Permanent Magnet Synchronous Motor(PMSM)utilize current as virtual variable which is not adaptive to the condition that accurate torque is needed. The paper propose a novel back-stepping algorithm regarding torque and flux linkage as virtual variable which can make the deviation between output torque of PMSM and load torque convergence to zero rapidly in on global scope and can make the control variable independent with the load inertia premising viscous friction neglected. The method which can be applied for the circumstance that load torque and moment of inertia is mobile possesses reference value to some extension.