Based on the existing measured data of an Floating Production Storage and Offloading (FPSO) in Bohai Sea, the multi-body dynamic characteristics analysis of the positioning system of a Marine Nuclear Power Platform (MNPP) is analyzed. A multi-body dynamic model of the MNPP positioning system is established. The Response Amplitude Operator (RAO) of the MNPP and a FPSO in Bohai Sea is used to derive the 6-degree of freedom response scale coefficient, and the Empirical Mode Decomposition (EMD) method is adopted to preserve the wave frequency components of the original data. On the top of that, the mooring recovery capability of the positioning system and the force behavior of each hinge joint are calculated. At the same time, the calculation results are compared with the force of the FPSO soft yoke mooring system, and the analysis results verify the rationality of the design of the nuclear power platform positioning system in the measured sea condition. It can provide a scientific analysis tool for the design and safe operation of the mooring structure of marine nuclear power platforms.