The displacement measuring system of giant magnetostrictive actuator is the basis of the study on its performance. In order to improve the accuracy of the test data, after building a displacement measuring system, the error models caused by the temperature changing, driver, displacement measuring system and acquisition subsystem were derived. The error synthesis model under these factors effect was given. The results of experiment and simulation show that when the displacement of giant magnetostrictive actuator is 18 μm，the relative errors of displacement acquisition subsystem, the subsystem used for driving actuator and the temperature changing is 056%,283%, 328%, and the relative error of displacement measuring system is 437%.