In this paper,the stability problems of coal and rock mass exerted by horizontaland vertical forces are studied with the help of the method of catastrophic theory. The expression ofthe total potential energy function for this system is derived. This system can be described by thecusp catastrophe model. The bifurcation set which makes this system to loss its stability in the hori-zontal and vertical force control space is obtained. At the same time ,the process of Sudden statechange of coal and rock due to the changes of horizontal and vertical forces is discussed.