Abstract: Aiming at the problems of too large calculation amount and poor computational efficiency when applying the methods of computational fluid dynamics (CFD) and three-dimensional refined modeling to the analysis of thermal-hydraulic behaviors of the fuel assemblies with mixing vane grids in pressurized water reactor (PWR), a virtual body force mathematical model was established based on the influence mechanism of the mixing vans on the flow and temperature fields in terms of flow resistance, flow diversion, fluid mixing and heat transfer enhancement to investigate the effect of the mixing vanes. The virtual body force model was added to a two-subchannel rod bundle model without mixing vane in the form of momentum source term, and the flow and temperature fields downstream of a mixed vane spacer grid were captured. This method significantly simplifies the modeling process, reduces the amount of calculation and improves the calculation efficiency. The effectiveness of the virtual body force model was verified through a comprehensive comparative analysis with experimental data and the calculation results of traditional body-fitted mesh modeling. The study shows that the comprehensive effects of the mixing vane spacer grid on the flow and temperature fields can be assumed to be that the mixing vanes exert a certain force on the fluid. The force changes the law of fluid particle motion, which is the reason causing special thermal-hydraulic behaviors. The key thermal-hydraulic parameters such as flow velocity, pressure drop and heat transfer coefficient calculated by the virtual body force model established are in good agreement with experimental data and calculation results of the body-fitted mesh modeling.