Considering the influence of convective heat transfer, a mathematical model of heat and mass transfer was established for the growth system of large-size SiC single crystal based on physical vapor transport method. The distribution of temperature field and gas phase flow field in the growth system was studied by numerical simulation. The results show that the temperature, temperature gradient and heating efficiency in the crucible will gradually decrease with the increase of coil turn spacing and coil diameter. The rotating crucible can effectively solve the non-uniformity of temperature field caused by the coil spiral shape. By continuously adjusting the relative position between the coil and the crucible, the optimal temperature field environment for high quality crystal growth can be ensured. In addition, the increase of the inner diameter of the crucible will aggravate the natural convection effect.