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.