The magnitude of door closing force is important in vehicle NVH characters, and in most case, it is not fully studied by computer aided engineering (CAE) in an early developing stage. The research took a heavy-duty truck as the study object and used Computational Fluid Dynamic (CFD) method with dynamic mesh to analyze the flow field of the cabin during door closing process. The change trend of pressure with time was obtained, and the influence of different factors was studied. The experiments were conducted to verify the results. Results show that the velocity of closing door and the size of relief holes have a significant influence on cabin interior pressure, and greater velocity leads to larger the pressure in cabin. The initial angle of the door affects interior pressure less comparing with the velocity of closing door. The interior pressure could be reduced effectively with the method of decreasing the velocity of closing door and increasing the size of relief holes.