Abstract: In this paper, neutral beam injection experimental unit system debugging and small size prototype verification test need vacuum environment support, according to the experimental gas load properties and vacuum requirements, exploring the development of an external refrigerator cryogenic pump. A cryogenic pump based on a 4 K cryocooler was designed, and the performance of the pumping unit was analyzed. ANSYS thermal analysis method was used to study the thermal performance of the pumping unit, and the temperature distribution under different gas thermal loads was obtained. The results showed that difficult-condensing gases such as H₂ and He could be effectively extracted when the temperature of the pumping surface was about 5 K. MOLFLOW was used to simulate the gas particle movement of the cryogenic pump connected to the pumping speed test system, the rationality of the pumping unit design was verified, and the trapping coefficient was 0.409. The influence of gas load on the pumping performance is investigated. The results show that the pumping speed of the pump fluctuates less under the influence of temperature rise, and the pumping performance is superb. Research methods and results provide a useful reference for the development of cryopumps for the NBI experimental test.