Abstract: According to the simulation loop of Integrated natural circulation reactor,the mathematical model of natural circulation in non-inertial reference system is established,and the influence mechanism of ocean condition upon natural circulation is analyzed.Software is programmed to investigate the behaviors in the cases of rolling without heating power,static state with different power and rolling with heating power, and calculation results show that:the inertia force added by rolling causes the periodical fluctuating of the flow rate of channels,but it is not the direct reason of core flow fluctuation.The heave changes the driving head,and causes the same flow rate fluctuation of all channels.Inclining makes the core flow rate decrease, but the change of flow rate of different channels is different.