Abstract: A mathematical model of contact heat transfer was build by the GW statistic contact model, and the results agree well with experimental data. By simplifying the rough interfaces, a model of radiation heat transfer between interfaces was constructed. The numerical results indicate that the effect of radiation heat transfer can not be neglected when the temperature of interfaces above 400 K. Nondimensional contact load has a larger influence on the conductive than the radiant conductivity, and for the non-contact area decreasing as the non-dimensional contact load increasing, the conductive conductivity increasing quickly and the radiant conductivity decreasing slowly. The influence of asperity slope on the equivalent radiation coefficient is the most important one among the geometric parameters of interfaces. At the same non-dimensional contact load, the smaller asperity slope the higher equivalent radiation coefficient. The numerical error-test of equivalent radiation coefficient shows that the order of the max relative error is 10^-3. Within the range of this paper, the equivalent radiation coefficient is only the function of interfaces' character and contact load. It has nothing to do with the temperature and temperature difference of interfaces. The equivalent radiation coefficient is an appropriate parameter to express the radiation intensity in contact heat transfer.