A type of displacement actuator used in active optics on Astronomical Telescope LAMOST was described in the paper. Now it have obtained success on the small LAMOST. Tests of the actuator using dual-frequency laser interferometer give some main parameters of them, and also give influence of condition varieties example for pull or push force. It show how do these conditons affect the actuator, and how to use the actuator to fit active optices. Finding out the characteristics after testing, these actuators were applied on the telescope. Some puzzles were encountered and solved all, which was showed in the paper. Finally we could control these actuators go forward or backward to several tens of nanometers accurately. By these technologic problems solved in the test and locations, these actuators could be applied on LAMOST or larger Astronomical Telescope.