Abstract: A typical body structure B-pillar was selected as the research object. Experiment and simulation analysis were used to investigate its optimization design method for resin transfer molding method (RTM) process. The injection mode was optimized by control the resin flow front, which could reduce the porosity and ensure the quality of the part. Firstly, the self-manufactured variable thickness permeability test mold was used to obtain the selected fabric permeability, then the robustness of the adopted simulation method and the obtained permeability data were verified by comparing the vacuum-assisted RTM experiments with the virtual simulations. Finally, combing the filing cycle and the porosity controlling theory, the optimal design of the injection port distribution and injection modes of RTM forming process were investigated. The results show that, for the selected automotive structure, the parts with the injection of optimized injection rate acquire the lowest porosity, but their filling cycles are too long, then the injection of a constant flow rate and two injection ports can better take into account the requirement of both the filling cycle and part porosity.