According to superposition compression arch structure and the interaction mechanical characteristics of cavern rock, based on limit equilibrium theory, set up reliability analysis model of large-span cavern of a high-stress mine. Using FOSM method determines the reliability index of the large-span and high-stress cavern. By the mean and variance calculations of simplistic variations parameters of construction features, geological investigate and rock mechanics of Jinchuan Mine large-span cavern obtains a suitable jinchuan mine's reliability index formula, and calculates the reliability index()of Jinchuan Ⅲ mine crashing cavern, the minimum value of 1.137. On the assumption that random variables of affecting the stability of the crashing cavern obey normal distribution, and the reliability index()and failure probability()have established relationship. According to the standard normal distribution function can be calculated less than the risk probability()of instability of the structure of 5.87%, that is the stability of the cavern is greater than 94.13% reliability to suffice the stability requirements of the cavern.