When the coal (rock) specimens are tested with infrared, one can observe that the specimens’ temperature field is changing. Commonly, causes of the changes are due to specimens’ plastic deformation and crack extension. But many coherent documents indicate that most specimens even has high temperature field after the peak strength. This paper put a forward that the influence of friction between the fracture planes on the specimens’ temperature field could not be ignored. Meanwhile, the paper gives a simple friction model of two blocks,. In the model, the friction surface plays the different roles to the two blocks as moving heat source and fixed heat source respectively. Those different heat sources have different effect on the blocks’ temperature field. In the end, analytic solutions of temperature change at any point of two blocks that caused by friction are given.