In order to achieve the function of active adjustment of primary reflector for the QiTai radio Telescope (QTT), a kind of high precision positioning actuator is designed and some performances of the prototype are tested. The actuator scheme adopts the stepping motor, angle sensor, ball screw and worm gear. The detail design and simulation for the key components are made, and their accuracy, electromagnetic compatibility and environmental adaptation are especially studied. Accuracy tests of prototypes are carried out, and the result indicates that the actuator can meet the requirement of positioning accuracy (15 μm). Moreover, the field test of environmental adaptability of actuator prototype has been carried out in Xinjiang for more than a year, and during the test the prototypes go well without any faults, they can meet the requirement of environmental suitability.