In order to accurately analyze high and steep arc slope security and stability in whole and in part, and provide references for high and steep slope design in open pit,finite difference strength reduction method is used to analyze slope stability and the whole slope safety coefficient is obtained.And calculation element safety degree is used to get the part slope safety coefficient.Convergence of maximum nodal displacement with time-step curves are adopted as slope stability failure criterion, and thus big errors caused by artificially specified tolerance when other criteria are used are avoided.Taking an iron mine southwest slope for example, we write strength reduction method, failure criterion and safety degree programme with FISH language and use the programme to calculate the problem.The results show that the methods of finite difference strength reduction, the failure criteria based on convergence of maximum nodal displacement with time-step curves and safety degree of calculation element is fit for studying stability of high and steep arc slope stability.At the same time, the method put forward a new idea for designing high and steep arc slope.