In order to ensure the normal operation of space inertial sensors in orbit, it is necessary to ensure the test mass is fixed during launch to prevent collision with the surrounding capacitor plate. It must grab the test mass after reaching its predetermined orbit and precisely release it in its correct position with minimal residual velocity such that it remains free-floating. In this paper, a piezoelectric linear actuator that is used to grab the test mass is designed, customized and tested for performance. The test results show that the customized piezoelectric actuator can achieve a minimum step size of less than 1 nm, but the step length stability error is large; the maximum driving force at 150 V of input is 72 N; the single stepping drive force is stable; during the process of fixing the test mass, the driving force is stable and the deviation in its stability is 0.16%. These findings meet the needs of the grabbing, positioning, and release mechanisms.