Abstract: One of cold-region roadbed cooling techniques is to install shading boards on the shoulder of the embankment over permafrost stratum. Most researches currently focus mainly on the temperature evolution of the roadbed under the board and on the optimal design of the board. The cooling mechanism of the board, however, is not available. The heat flux balance between the board and the shoulder is simulated, and the model is validated using the measured data from an in-situ shading board. The results show that the cooling effects of the board can be greatly promoted by decreasing the thermal emissivity of the lower surface of the board, and/ or can be possibly enhanced by increasing the albedo of the upper surface of the board. Increasing the wind under the board, however, may contribute negligibly to the cooling effects. This means that installing the board as closely as to the shoulder surface and decreasing the thermal emissivity of the lower surface of the board can both promote the cooling effects and prevent the board from wind damage simultaneously.