A dynamic-force extraction, based on the least-squares method, is proposed for micro-propulsion testing. Having modeled the displacement oscillation of a micro-newton torsional pendulum, the time evolution of the dynamic force may be calculated if the stand constants are well calibrated. According to the linear characteristic of the motion equation, a reconstruction of the dynamic thrust reduces to solving linear equations. The simulation analysis shows that the error is affected by the sensor noise and the low-pass filter as well as the sampling rate. Validation experiments were performed showing that this method reconstructs the dynamic force well up to 8 Hz with an error less than 15 mu N. The noise-induced error moreover varies little with frequency. (c) 2018 Author(s).