Abstract: With the continuous increase of the aperture of optical astronomical telescopes, the main mirror of the telescope is mostly in the form of spliced mirrors, and the micro-displacement actuator, as a key component of the mirror splicing technology, has always been one of the research hotspots. In this paper, a double-helix ball screw is used to replace the reducer plus ball screw structure in the traditional mechanical micro-displacement actuator. The differential screw principle is used for micro-displacement output, and the servo motor is used as the driving motor, and the torque required by the motor under load is analyzed. This research starts from the requirements of output displacement accuracy, output range and bearing capacity and carry out performance tests. The experimental results show that the total stroke of the micro-displacement actuator is 5 mm, the theoretical maximum load capacity is 1 200 N, and the step resolution of 200 nm can be realized under the load of 200 N. The accuracy of open-loop unidirectional displacement is better than 0.65 μm, and the accuracy of closed-loop unidirectional displacement is better than 0.2 μm, verifying that the proposed micro-displacement actuator scheme meets the requirements of high precision, large stroke and high load, and provides technology for the design of large-aperture astronomical telescopes for future reserve of our nation.