As a common electrical fault, single-phase grounding fault will distort the DC voltage ripple of ship medium voltage DC power system and affect the normal operation of the system. Taking the single-phase grounding fault in medium voltage DC power system as the research background, we study the influence of neutral grounding mode of rectifier generator on ripple. Firstly, using the symmetrical component method and the switching function method, the normal ripple order of DC voltage and the ripple order under fault are calculated respectively, and the analytical expression of AC component in DC voltage under fault is derived. Then, by analyzing the zero sequence circuit between windings, the correlation between the zero sequence voltage of fault winding and grounding mode is obtained, which can be used to further study the influence of grounding mode on DC ripple. Finally, the model is built by PSCAD and MATLAB/Simulink simulation software for verification. This research can provide a reference basis for the selection of grounding mode of rectifier generator in ship medium voltage DC system.