To achieve fast Monte Carlo ray tracing on CAD models, a Bi-level Spatial Subdivision based ray tracing method (BSS) is proposed in this paper. This method was implemented and integrated in Super Monte Carlo Program for Nuclear and Radiation Simulation (SuperMC) and tested on ITER Benchmark and Force-Free Helical Reactor (FFHR) model. The testing results on ITER Benchmark model demonstrate the correctness of this method. The testing results on FFHR demonstrate that this method can save most of the preprocessing work to greatly improve the Monte Carlo analysis efficiency. Both results reveal that this method achieves applicable calculation speed comparing to the traditional Constructive Solid Geometry (CSG) broadly used in Monte Carlo codes.