The properties of silica fume concrete in natural sea water are studied, with special focus on the relationship between the freezethaw durability and chloride ion diffusion coefficients. The influence of various factors on concrete resistance to frost and chloride diffusion is studied, including the watercement ratio, equivalent silica fume dosage substitution for cement, and the amount of airentraining agent and compared with that of ordinary concrete. The results show that adding silica fume cannot improve the frost resistance of concrete but it increases resistance to chloride diffusion. Both the frost resistance and chloride diffusion properties can be improved simultaneously when silica fume is used with an airentraining agent. A silica fume content of approximately 10% is the optimum value for the composite resistance to frost and chloride diffusion. A new assessment method (Rvalue method) is proposed to evaluate the composite properties of frost resistance and chloride diffusion of marine concrete.