The application of passive safety systems (PSSs) can greatly improve the safety level of the Offshore Floating Nuclear Power Plants. As one of the important component of PSSs, the secondary passive residual heat removal system can be seen as the multiple natural circulation (NC) loops coupled system. The transient response characteristics between coupled natural circulation loops may affect the core decay heat removal progress under accident conditions. Besides, the ship motions caused by ocean waves can induce oscillations of the system parameters and variations of the reactor thermal hydraulic characteristics. The superposition effects of the transient response characteristics of the multiple NC loops coupled system and the system parameters fluctuation caused by ocean conditions can generate more complex system behaviors. In this paper, effects of the transient response of key parameters during process of increasing power in coupled natural circulation loops under ocean condition was analyzed by the modified RELAP5 code. The simulation results show that the response time of each parameter of the system changes greatly under inclination and rolling condition, but the effect of pitching and heaving motion on the response time of multi-loop natural circulation system is basically negligible.