In order to study the heat exchange characteristics of high temperature mixed gas in tube heat exchanger, a three-dimensional steady state numerical model based on the k-ε turbulence model, heat transfer theory and Maxwell-Stefan diffusion theory was established to investigate the influence of material diffusion on the temperature field distribution of heat exchanger. The heat exchanger was then parametrically analyzed involving the inlet temperature and velocity of cold and heat fluid and its heat transfer efficiency was examined from the view of exergy. The results show that the substance diffusion changes the distribution of the components in the heat flow mixed gas and the hydrogen which is dominant in the heat transfer diffuses reversely, exchanges heat repeatedly, thus consuming the heat of high temperature fluid, leading to a reduced level of the heat transfer performance of heat exchanger. The equivalent heat transfer coefficient reduces from 16.564 W/(m²·K) to 15.955 W/(m²·K). Within a certain range of operating parameters, the exergy efficiency of heat exchanger is between 10% and 30%, and the cooling effect is obvious.