In tunnel design and construction, the stability evaluation of tunnel roof wedge usually adopts traditional deterministic analysis methods, which cannot appropriately reflect the spatial variability of rock mass. Based on limit equilibrium method, an efficient approach for evaluating the safety factor integral expression of tunnel roof wedge is presented in this study. This approach considers the influence of spatial variability of rock mass joint friction angle and is validated by universal distinct element code (UDEC). Based on random field method and Monte Carlo simulation (MCS), a generated random field is substituted into the established safety factor integral expression to calculate the safety factor of the tunnel wedge, in which the spatial variability of rock mass joint friction angle is well considered. The failure probability of roof wedge is calculated with consideration of geological and geometry parameters uncertainties. The results indicate that the spatial variability of rock mass joint friction angle has a significant influence on the failure probability of tunnel roof wedge. Ignoring the spatial variability of rock mass mechanical parameters will cause an overestimated failure probability of tunnel roof wedge.