One of the important factors for collapse of thin and unstable rock block is temperature in the areas with large temperature difference. This paper will consider the effect of stability on unstable rock block under the combination of temperature and stress. Firstly

calculating the temperature transfer in x and y direction respectively on the basis of the heat transfer method

and then establishing the computing method of temperature stress in temperature field and master structure plane of unstable rock mass by using superposition principle. Considering the combination of temperature stress

the unstable rock mass weight

earthquake and fissure water pressure

we established the calculation method of stress intensity factor of the master structure plane of unstable rock mass based on fracture mechanics

and then according to combination stress intensity factor of the master structure plane of unstable rock mass and fracture toughness to construct the stability analysis method of unstable rock mass. The comparative analysis shows that temperature stress has a significant influence on stability of thin and unstable rock mass. At the beginning of temperature rising

the stability coefficient of unstable rock mass decreases quickly

and with the temperature rising further

the stability coefficient of unstable rock mass changes slowly

which reveals the stability variation law of unstable rock block under the combined action of temperature and the perforation’s length of master control structure plane. The stability coefficient compute method of unstable rock mass in this paper can provide new approach to stability analysis of thin and unstable rock block in large temperature difference areas.