Abstract: To ensure the vitality of naval nuclear power at all times, the natural cycle lead-bismuth reactor loop will take partial loop operation when it fails under marine conditions. However, there are few studies on the partial loop operation characteristics of lead-bismuth reactor under marine conditions. Based on the secondary development of RELAP5/MOD3.1 program, the off-loop operation characteristics of a 10 MW natural cycle lead-bismuth reactor under typical oceanic conditions are analyzed. The analysis results show that the system parameters of the reactor are less sensitive to the change of tilt angle when the reactor is operating under inclined conditions. Under undulating conditions, the fluctuation of flow rate is reduced by 9% and the outlet temperature is reduced by about 16 K. The larger the undulating amplitude, the more drastic the flow rate fluctuation; the larger the undulating period, the more obvious the flow rate oscillation, but the effect is also weakening. Under rocking conditions, the core flow and outlet temperature are reduced and the reactor introduces higher safety margins. The larger the swing amplitude and the smaller the swing period, the larger the flow fluctuation, and the core outlet temperature is significantly more sensitive to the cycle change than the swing amplitude change.