Abstract: In order to analyze the structural safety of fuel assembly for floating nuclear plant under marine environment, the structural loads of fuel assembly in two states of working in reactor and refueling at sea were researched by means of combining hydrodynamics and structural mechanics. Taking the ship random motion response under marine environment into account, the structural safety of fuel assembly working in reactor was checked and the theoretical basis for the feasibility of implementing refueling operation at sea was provided. Taking the marine nuclear power platform as an example, firstly the time domain simulation aiming at platform was conducted to obtain the time serial curves of center of gravity in six degrees of freedom, and then remote displacement method was adopted to transfer the ship motion to the reactor to realize the numerical simulation of reactor moving with the ship, and the maximum values of stress and strain of fuel assembly were calculated finally. The results show that the maximum values of stress and strain of fuel assembly increase obviously in ship moving state compared with in static state, which explains that it is quite essential to consider the ship random motion response during the structural safety analysis of fuel assembly.