Based on the thermodynamics principle, a simple thermal model of steel plate and rubber cloth was established, thus their temperature changes in a day are calculated. The results show that the surface temperature of the rubber cloth can be acquired by solving the thermal equilibrium equation; the steel plate thickness can strongly affect the plate temperature changes within a day. (The thicker the plat, the smoother the temperature change is, and the more thin, the more it approaches to nature rubber. )The surface emissivity affects the temperature of the steel plate or the rubber cloth in the same way but the absorbing factor plays the opposite effect on the steel plate or the rubber cloth compared with the emissivity and it affects merely in daylight.