Abstract: Rock mass with intermittent joints can be treated neither as a distinct block structure nor as a complete continuous medium.So the usual stochastic model of block theories or continuum theories can not be used.Since both rock bridges and joints are present in rock masses,the failure probability of rock masses is related to their statistical properties. After the probability distributions of strength parameters for joints and rock are proposed,the stochastic model of fracture is inferred in this paper.The susceptibility of several joint parameters in strength criterion is analyzed.Finally,a suggestion for geotechnical engineers is represented in the paper.