In the process of scientific drilling, to ensure the basic verticality of the upper section of the ultra deep hole is the prerequisite for drilling the ultra deep hole to the target layer smoothly. Many drilling projects have to be completed prematurely, where the boreholes can not drill to the expected target depth due to the uncontrollable hole deviation. The availability of automatic vertical drilling tools breaks the limitation of traditional deviation prevention and correction methods, and drives the well deviation control technology to develop rapidly. At present, the actuator diameter of vertical drilling tools is large, the required displacement is high, the response speed is slow, and the whole performance test can only be carried out on the stable platform. This paper introduces a new small diameter actuator which uses mud pressure difference as the power source with the design of its performance test system. The internal pressure, pushing force, discharge and response speed of the new actuator were tested on the system separately, and the results showed that the new actuator had the advantages of small structure, high efficiency, small displacement and fast response. The test system can verify the feasibility of the new actuator before testing the whole prototype of the vertical drilling tool.