It is known that the automobile cabin thermal comfort, could keep the driver and passengers feel better which has a great effect on traffic safety. In this paper, to the FAW truck cab, we did some researches about automobile cabin thermal comfort. Our plan is to calculate the air flow distribution and the temperature in steady and transient state when there is warm or cool air flow. The heating and cooling experiment methods standard of cabin are based on the national standard and the automobile industry standard of China. Then the numerical simulation process becomes very important. So we used the commercial CFD code- STAR-CCM+ for study in this paper. Firstly, Geometry Clean up. Secondly, Wrap and Remesh, we chose the internal surface at the wrap surface of cabin and air conditioning pipes, then we remesh the surface. Thirdly, generate the volume mesh which is polyhedral mesh, and the number of the volume mesh is 9.4 millions. The boundary layer of the cab and pipes are so different that we should redefine the boundary layer. Fourthly, Calculation, in the process of the numerical simulation, we calculated the pipes separately at first, and counted the flow rate of every air outlet. Then we put the pipes and the cabin together for calculating and simulate the flow. Compared the later air flow rate with the former one, we can identify if it is necessary to calculate the pipes separately. The thermal Comfort Wizard includes: crew attribute definitions, thermal calculation solver advanced settings and thermal calculation boundary condition settings. Here the occupant height is 1.75 m, the clothing thermal resistance is 0.05 K m2/W. We don't take the cabin body leakage into account in this paper. Finally, it is the analysis of the thermal comfort at cooling condition. We improved the shape of streamline pipes, added the cooling air of the driver, and made the flow surround the foot of guest. By analyzing the flow rate and the temperature data at each measuring position, we can get the air outlet flow field at the middle of the dash board, which near the driver, effected the temperature around the driver most, so we should take some measures to improve that condition.