Aiming at the problem of the concentrating solar cell efficiency restricted by the temperature. The closed two-phase thermosyphon could be used for heat dissipation in concentrat- ing solar cell with high heat flux, then water was selected as the working fluid. Numerical computation methods were adopted to study heat transfer performance of the finned heat pipe radiator in free convection. The temperature field, velocity field, total heat dissipating capacity of different fin pitch and side length as well as free convection heat transfer coefficient under the condition of constant temperature of parent tube were obtained. As a result, the fin side length had greater impact on the natural convection heat transfer coefficient and average total heat flux per unit area; the fin pitch had greater impact on the finned heat pipe radiator total heat dissipating capacity per unit length; the finned heat pipe radiator was the best when fin pitch was 3mm and fin side length was 90mm.