Abstract: An automatic modeling method which can import three-dimensional CAD models into Geant4 was implemented using open-source CADMesh interface program in order to carry out the Monte Carlo simulation research of complex structure sites’ radiation field. A waste disposal facility was automatically modeled and then the distribution of ambient dose equivalent rate was simulated using the built-in command-based scoring in Geant4. The simulation results of ambient dose equivalent rate distribution were compared with the actual measurement results. It shows good agreements between simulation results and the measurement results within 50% error. The applicability of the automatic modeling method was validated preliminarily.