Abstract：The mechanical process and characteristics of slope stability based on Spencer analytical pattern are introduced firstly；and the calculation flowchart of safety factor is also given. It is found that the difficulty in slope stability analysis with Spencer analytical pattern is that the partial derivatives can not be computed because the safety is an implicit function. So difference method is introduced to solve the partial derivatives approximately. Based on the derivation of compound function，the formula of each item of partial derivative and the iterative method with linear approximation to compute reliability are deduced under the condition that design point method is used to obtain the reliability of slope stability based on Spencer analytical patterns. According to the above-mentioned research，seven steps to analyze reliability of slope stability by the design point method based on Spencer analytical pattern and concrete method of each step are given. At last an engineering example is analyzed with the method；and the result is compared with that obtained by Monte Carlo method. It is shown that the results obtained from the two methods are similar and the precision satisfies engineering request；and the workload of the introduced method is much little than that of Monte Carlo method. So it will be greatly valuable to engineering practice.
