In order to solve the problem of dynamic measurement of mN-level thrust output by electric thruster, a micro force measurement device based on piezoelectric torque sensor is developed in this paper. By converting the “little force-large force arm” of the thruster into the “little force arm-large force” of the measuring end, the tiny force output from the thruster is converted into torque measurement, and the measurement of the mN-level tiny force is realized. The measuring device is statically calibrated by applying a standard tiny force with electromagnetic force; the nonlinear error and repeatability error are 1.26% and 1.43% respectively. The natural frequency of the measuring device in the thrust measurement direction is 35 Hz by the pulse excitation response experiment method. The test result shows that the proposed device is feasible to measure the micro output force of mN-level electric thrusters.