Abstract: We propose a novel method of second harmonic multi-beam laser heterodyne measurement for micro impulse based on oscillating mirror sinusoidal modulation. The measurement of the micro impulse, which is converted into the measurement of the small tuning angle of the torsion pendulum, is realized by measuring the interaction between pulse laser and working medium. Based on Doppler effect and heterodyne technology, loading the information of small tuning angle to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, this method can obtain value of small tuning angle after the multi-beam laser heterodyne signal demodulation. Processing the weighted-average of multiple measurements improves the accuracy of small tuning angle values and eventually the precise value of micro impulse is calculated. Using Polyvinylchlorid+2%C as a working medium, this novel method is used to simulate the micro impulse generated by the interaction between the pulse laser and the working medium by MATLAB, the result shows that the relative error of this method is just 0.8%.