This paper presents a novel pressure-resistant oil-immersed proportional actuator with a magnetic grid magnetic-isolated ring (MGMR) on its single-piece sleeve. A two-dimensional finite element method is used to establish the model and analyze the static and dynamic performance. The experimental and simulation results agree well with each other and verify the static and dynamic performance characteristics of this proportional actuator. The results indicate that the actuator can produce 15 N force output when the ampere turns is 450AT in 2.2-mm wide working stroke; the rising step response time and the falling step response time are 24 and 17 ms, respectively, and the frequency response (−3dB) is 25 Hz. Consequently, its applications to electrohydraulic proportional/servo valve are acceptable.