Abstract: Establishing a crew dose assessment system is one of the key techniques to be solved urgently in the development planning of the nuclear power mechant ships in China. Research was carried out on large nuclear-powered ships with the largest number of crew members, the most complex staffing and the widest coverage of radiation protection. A dose assessment system for crew memebers on large nuclear power ship is given in this paper. The dose assessment system is constructed according to the methods recommended by International Commission on Radiological Protection and International Atomic EnergAgency, including basic dose quantities, dose limits and reference levels, and dose calculation and measurement, covering planned exposure and potential exposure, which can meet the demand of crew dose assessment in forecast dose, actual dose and review. Further more, the detailed measures used to estimate the crew dose is presented in the dose assessment system, such as the radiation sources and exposure pathways need to be considered, the model, quantity and values should be applied.