Abstract: Objectives Conduct research on the stability issues of ship DC propulsion systems with a high proportion of power electronic devices. Methods The ship's DC propulsion system is composed of a rectifier, inverter, and propulsion motor cascaded together. The proportion of power electronic devices is large, which leads to poor stability of the DC bus. Based on the Middlebrook impedance stability criterion, a method is adopted to simplify the system model, linearize the nonlinear system, and transform the dq of the three-phase AC system into DC. The small signal output impedance of the DC bus and the small signal input impedance models of the inverter and motor are derived, laying a model foundation for analyzing the stability of the system; And optimize the controller parameters through particle swarm optimization algorithm to minimize the value of support capacitance while ensuring stability. Results On the basis of the simulation model of the ship's DC propulsion system built, the influence characteristics of the equivalent resistance and equivalent inductance of the supporting capacitor and DC bus on system stability were studied. The simulation results showed that the method of using particle swarm optimization algorithm to optimize controller parameters can significantly improve system stability margin, thus reducing the value of the supporting capacitor.Conclusions Theoretical research and simulation results show that the method of using Middlebrook impedance ratio stability criterion to study the stability of ship DC propulsion systems can be extended to the research of voltage oscillation and its suppression in comprehensive power systems with a serious proportion of power electronics. Using particle swarm optimization controller parameters can reduce the value of support capacitance while ensuring bus voltage stability, which has significant practical significance for reducing the overall size of ship DC propulsion system inverters.