In high speed and high precision machining applications,it is important to monitor the machining process in order to ensure high product quality.For this purpose,it is essential to develop a dynamometer with high sensitivity and high natural frequency which is suited to these conditions.This paper describes the design,calibration and performance of a milling torque sensor based on piezoresistive MEMS strain.A detailed design study is carried out in detail to optimize the two mutually-contradictory indicators sensitivity and natural frequency.The developed torque sensor principally consists of a thin-walled cylinder,and apiezoresistive MEMS strain gauge bonded on the surface of the sensing element where the shear strain is maximum.The strain gauge include eight piezoresistances and four are connected in a full Wheatstone circuit bridge,which is used to measure the applied torque force during machining procedures.Experimental static calibration results show that the sensitivity of torque sensor has been improved to 0.13 mv/Nm.A modal impact test indicates that the natural frequency of torque sensor reaches 1216 Hz,which is suitable for high speed machining processes.The dynamic test results indicate that the developed torque sensor is stable and practical for monitoring the milling.