Abstract: Due to complicated structure and the coupling and variety of heat transfer in the flat finned tube, it is difficult to obtain and analyze the local characteristics of in-tube heat and flow with the traditional experimental and correlation methods. Based on the distributed parameter thermo-dynamic theory, a coupled heat transfer model is proposed to the heat transfer between the two-phase fluid and the cooling air. The model is applied to a 1 m length engineering tube, and the temperature, heat flux, heat transfer coefficient (HTC), film thickness, shear and pressure-drop are characterized with the computational fluid dynamics solution. It is found that the condensation heat flux decreased sharply with the lateral flow of the cooling air, from 20, 000w/m² at the air inlet to 5, 000w/m² at the outlet; meanwhile, the welder layer play a key role to export the condensation-released heat to cooling-air with the heat flux up to 14, 000w/m², more attention should be paid to the heat-enhanced effects on the finned tube from the material and configuration related to the welder layer. The pattern of two-phase fluid inside tube is verified as the annular flow, and the film thickness is found to be increasing in the range of 16−25μm with the flow of two-phase fluid, due to the inclined tube configuration that effectively converges the condensate from the plate to the lower semicircle. Consequently, both the heat flux and HTC do not decrease lengthwise, agreeing well with the result on the corresponding section of an experimental tube.