Abstract: Constructive solid geometry (CSG) is usually used to model in traditional Monte Carlo programs. However, it is very difficult and time-consuming to use CSG to accurately model some complex high-order surfaces. In order to solve this problem, a Monte Carlo method (direct accelerated geometry Monte Carlo, DAGMC) that directly used CAD geometric modeling was proposed to perform particle transport calculations. Based on Monte Carlo program RMC, the DAG-RMC program using CAD geometry was developed, and three models of block assembly, fuel rod and Utah teapot were calculated and analysed using DAG-RMC program. The results show that the calculation results of DAG-RMC are in good agreement with the results of the traditional CSG modeling method and OpenMC program, verifying the correctness of the DAG-RMC in particle transport and critical calculation.