Abstract: During the marine nuclear power plant operation in harsh ocean environment,the large rocking motion of ship hull can induce condensate sloshing and pressure fluctuation in the condenser hot well,which has harmful effects on the operation safety of the condensate system.Hence,the transient flow and pressure fluctuation characteristics in the condenser hot well of the floating nuclear power plant are investigated by CFD numerical method under three rolling motion and three pitching motion.The results show that the condensation water pressure in the condenser hot well fluctuates periodically due to the rocking motion.The periods of pressure fluctuation and rolling motion are identical,whereas the fluctuation amplitude increases with the decreasing of the rolling motion period.Under the effect of rocking motion with small period,the inlet pressure of the condensate system falls below the minimal anti-cavitation pressure,which leads to potential cavitation hazard of the condensate system.The violent sloshing of condensation water level as well as the transient variation of mass force effecting on condensation water under rocking motion are two important factors for the transient thermal hydraulic characteristics in the condenser hot well.