Abstract: Based on the impulse measuring principle of torsion balance, a kind of laser interference differential method of micro impulse was advanced. The system setting and measurement procedure were introduced. The torsion balance structure design parameters were given. The calibration and verification were put forward. The system resolution, measurement range and precision were calculated. In the typical measurement condition, the micro impulse generated by the laser ablation was measured with the method, the typical result was given and analyzed. The results show that the system resolution of the method is competent for the 10-7 Ns magnitude, the measurement range covers five magnitudes, the maximum magnitude is 10-2 Ns with precision better than 95%.