A simple and direct limiting deformation equilibrium method for wedge sliding considering all the three deformation components of the discontinuity planes is presented. The traditional limiting equilibrium method is based on a statistic system assuming that sliding is resisted only by the sliding resistance parallel to the sliding direction along the line of intersection of the two discontinuity planes. Therefore, we work out the psudo-elastic system to take care of the deformation of the discontinuities and to solve the indeterminate system. Through analysis and experiment, it is illustrated that the result based on traditional method is unsafe. The calculated results are fairly consistent with the experimental ones, while those based on the traditional method are unsafe. The stiffness of the discontinuities should be emphasized.