In order to detect the impact energy generated by spacecraft micro-impact, a femtosecond fiber grating impact detection system for spacecraft micro-impact was designed and the impact energy was detected. The strain sensing model and edge filtering demodulation model of femtosecond fiber grating are established. The finite element analysis software is used to simulate the impact energy distribution of micro-collisions. An impact detection system was built to test the impact energy sensing characteristics of femtosecond fiber grating, and the energy transfer characteristics were analyzed by using the time-domain envelope extraction method. Experimental results show that when the balls with the mass of 10, 20, 40, 60 and 80 g fall at the same position, the collision signals detected by the grating system show a linear increasing trend, the maximum impulse voltage retrieved by edge filtering algorithm is 30. 8 mV. When the same mass ball falls at different positions, the collision signals detected by the grating system show a linear downward trend, the detected impulse voltage can be as low as 16. 5 mV. The system can detect the impact energy generated by the micro-collision, which has a certain reference significance to the problem of spacecraft micro-collision detection.