Abstract: In order to study the thermal-hydraulic characteristics of the lead-bismuth reactor under moving conditions, the transient analysis system program for the lead-bismuth reactor was developed, and the numerical model of the designed 5 MW natural circulation small modular lead-bismuth reactor was completed. The results show that under inclined conditions, the core mass flow rate decreases and the core outlet temperature increases. At the maximum inclined angle, the mass flow rate decreases by 20% and the core outlet temperature increases by 20 ℃. Under heaving conditions, the larger the fluctuation amplitude and the fluctuation period are, the greater impact on the reactor will be. Due to the flow resistance, the flow rate change has a delay of less than 1 s compared to the additional acceleration. Under rolling conditions, larger rolling amplitude angle and smaller rolling period will induce greater influence on the reactor. The peak temperature of the fuel cladding is within 20 ℃ higher than the steady-state value, which has little effect on the safety of the reactor.