Abstract：A calculation method of reliability for slope stability，whose state function is implicit function，was researched. The Janbu method as an example for the calculation procedure and process of stability coefficient of slope，in which mechanical model sliding surface is deemed as a non-circle，was introduced firstly. It was put out that the calculation for the stability coefficient of the mechanical model of implicit function was regarded as a test method. The implicit equation of calculation stability coefficient was taken place by an approximate equation that was fit through test results by response surface method idea. The limit state equation was established by using the approximate equation；and checking point and reliability indices were calculated. The approximate equation of calculation stability coefficient was combined with implicit function and the checking point to decide a new basic point and the sample points. New approximate equation and reliability indices were performed circularly until the reliability index was converged. The approximate calculation method of stability reliability for slope whose state function was implicit function was established. The accuracy of the approximate method was validated through comparison between reliability indices calculated by different methods. A stability reliability of open pit slope was analyzed by the approximate method at last.
