To cope with the problem of overheating of rear-mounted engine cabin, based on a type of hybrid vehicle, a coupled model for the cooling system of rear-mounted engine cabin was established by using the coupling 3D/1D model. Through the process of coupled calculation, the convection heat transfer coefficient of engine surfaces and the flow coefficient of engine cabin in different ambient temperatures and driving speeds were studied. In addition, the general laws of the heat transfer coefficient and the flow coefficient were summarized and empirical equations were provided. All the results proved basic parameters for the establishment of one-dimensional model and theoretical basis for the design of the engine cabin. By analyzing the heat flow field, it was found that convection heat transfer coefficient and flow field changed noticeably with different layouts of engine cabin. The increase of the area of ventilated grille in the rear of engine cabin or adjusting the layout of radiator reasonably can improve the uniformity of the heat flow field and enhance the capacity of convective heat transfer of engine surfaces.