Abstract: Under most condition,in calculation of stability coefficient of slope with various sliding model,an implicit expression was used.Then it was impossible to establish corresponding limit state equation while reliability of slope was studied.To solve is problem,an improved response surface method was researched.A slope stability analysis model of random sliding surface was used as an example of the improved response surface method.In the improved response surface method,calculation method of implicit stability coefficient of random sliding surface model replaced the finite element method of classical response surface model.To eliminate errors aroused by linearization of approximative response surface method function during calculation of reliability in classical response surface method,solution of checking point and reliability index by optimization principle of grades decline method was deducted.Calculation procedure of reliability index as well as fitting of approximative response surface function of improved response surface method was given.A practical example was analyzed by the IRSM at last.Calculation process of the IRSM was much more simple and its efficiency was much higher than classical RSM.