Abstract: The newly designed marine DC circuit breaker closing device must meet the requirements of small size, fast action, stable and reliable static maintenance. The design scheme of the closing device with the combined action of electromagnet and tripping frame is selected, and its action characteristics are studied. The mathematical equations of electromagnetic force and mechanical motion of the closing device are established; the finite element simulation model of the core component electromagnet is constructed, and the changes of electricity, magnetism, force, displacement and speed are simulated and analyzed; and this is used as input conditions, an ANSYS co-simulation model of the tripping frame with the lowest structural strength is established, and it is verified that the structural stress during the closing process is less than the Von Mises yield limit. The current and displacement data of the simulation and prototype experiments are compared and analyzed. The results show that when the power supply is AC 220 V 50 Hz full-wave rectification, the closing device can complete a 6 mm stroke within 19.6 ms, which verifies the correctness of the simulation results. The innovation of this paper is to design a set of small structure, simple and practical locking trip mechanical device, engineering application results show that its performance is reliable. The new scheme provides a reference for the design of marine DC circuit breaker closing device.