Abstract: This paper proposed a novel current control strategy that ensures maximum torque capability over the whole speed range for induction machines which widely used in industry applications,especially in spindle drive systems of machine tool in recent years.Considering voltage ratings of the power inverter,the current constraint of the induction machine and the limit of maximum slip frequency adequately,the optimal current vector locus for maximum torque operation was derived by mathematical method,based on which the guidelines for the implementation of current optimizing strategy was summarized.Then,following the design guidelines an alternative control algorithm was developed,which could guarantee the good smooth transition between constant torque region and flux-weakening regions.Experimental results were presented to verify the validity of the analysis,which achieves the maximum torque operation over a wide speed range and the highly dynamic response performance.