[en] In this study, a sensitivity analysis on shear failure of a discontinuity adjacent to a circular opening has been performed based on a series system reliability analysis. To realize the failure surface of the system, Mohr-Coulomb yield criteria and other empirical models suggested by Jaeger, Ladanyi and Archambault, and Barton and Bandis have been adopted. Discontinuity direction, initial stress, pore water pressure and various physical properties obtainable from site investigation and Lab. test in discontinuous rock mass before the design stage are selected as multi-random variables, all of which could be simulated in terms of normal distribution, log-normal distribution, or beta distribution. In order to obtain generalized reliability index and failure probability, FORM(First-order reliability method) and PNET method have been adopted with modified HL-RF method as for an optimization scheme. A computer program has been developed and verified by comparing the analysis results by Monte Carlo simulation. The effect on probability of failure of cavern size, distance between a cavern and a discontinuity, and correlation coefficients have been reviewed through reliability analysis. The most sensitive parameter on system failure has been obtained through sensitivity study