SF6 gas insulated transformer (GIT) has the advantages of nonflammable and non-explosive. However, there is a deviation in flows near the coils, which results the coil temperature overheat. In order to remove the deviation of flow, it is necessary to use force-directed-gas duct cooling system. In this paper, the force-directed-gas duct heat fluid coupled finite element method is presented based on the fundamental theories of heat transfer and fluid dynamics, a standard k-epsiv model was used as a turbulence model, the components of gas flow and the coils temperature distributions are also calculated. Additionally, the force-directed-gas duct design method is presented.