To grasp the effect of normal overload on the airborne thermoelectric conversion system, the convective heat transfer process of working fluid in heat exchange ducts was simulated on the basis of the computational fluid dynamics software. Results show that the growth of normal overload makes the flow field structure inside the pipeline changed, which finally leads to the gradually decreasing wall temperature. Along the duct, the formation of one wall temperature peak of the heat absorption channel is closely related to the change of turbulent heat flux near the heated wall. When the normal overload increases from 0g to 2g, the flow structure at the front end of the heat absorption channel changes from 8 vortexes converts to the two main vortexes structure and the influence of secondary flow is gradually increasing, the formation of the two main vortexes makes turbulent heat flux of fluid near the heated wall increases gradually due to the thinner temperature boundary layer. Hence, local heat transfer coefficient can be increased by 80%. With the enhancement of heat transfer in duct, the wall temperature of the heat absorption channel decreases and the maximum of wall temperature drop can be up to 290 K.