Abstract: The small research reactor which exhibits the features of high heterogeneity, strong absorption regions and complicated geometry challenges the numerical computation capabilities of existing neutronics codes. To overcome the restriction of geometry, the transport code MOCAGE, based on the constructive solid geometry formulation（CSG） and matrix method of characteristics, has been developed in the present study, and the track tracing has been parallelized applying the OpenMP programming model. The irregular geometry problem and HTTR benchmark problem with three configurations of control rods has been used to verify the capability of characteristic line tracing and to evaluate the code’s numerical accuracy for complicated geometry. The system effective multiplication factor, the normalized fission densities of fuel pins, and the normalized neutron absorption densities of burnable poison rods and control rods have been calculated by the developed code. Meanwhile the comparison with MCNP5 reference solutions has been performed, and the results demonstrated that the developed code can model the complicated geometry and trace the characteristic lines correctly, and excellent agreements were achieved with respect to the aforementioned parameters. The time consumption of tracing procedure has been reduced significantly using the OpenMP.