Abstract: China Fusion Engineering Experimental Reactor (CFETR) is an important scientific project designed and developed independently in China. CFETR aims to connect and supplement with ITER and provide necessary technology for the development of DEMO grade fusion reactor power station. Monte Carlo method plays an important role in the fusion neutronics and shielding design of fusion reactor. In this paper, the mathematic model and computing method of complex surface modeling of Monte Carlo code were studied and the function was developed in the selfdeveloped Monte Carlo code cosRMC. The correctness of this function was verified by PPCS (power plant conceptual study) model. Then a threedimensional refined model of CFETR was constructed and used to calculate and analyze the key neutronics parameters in the design of CFETR blanket. The results show that the tritium breeding ratio, neutron wall loading and the nuclear heat deposition are in good agreement with those calculated by MCNP, and the relative discrepancies are all within 5%, which meets the requirements of engineering design. The applications of cosRMC for neutronics analysis of fusion reactor cladding are proved to be correct and effective. The analysis of neutronics parameter of CFETR also provides the reference for its designs and optimizations.