By theoretical calculation, it is found that the same earth temperature gradient leads to the greater difference of temperature stress in different kind of rocks. In calculating ground stress of underground mines, the influence of earth temperature gradient on some kind of rocks can be neglected; but the temperature stress caused by earth temperature gradient in some other kind of rocks are considerable and must be considered, otherwise the hidden danger may exist or even serious safety accidents such as collapse of surrounding rocks may appear in the process of mine extraction. The correctness of the result obtained by the theoretical computation is verified in the experiment of reinforcing the hanging wall of stope with cable bolt in Dongxiang Copper Mine.