The design and safety evaluation of a geotechnical project is influenced by the shear strength parameters of geo-material. Moment method and linear regression method are the mainly used methods to estimate the shear strength parameters. But moment method is always over estimate the variation of strength parameters due to the smaller sample size, meanwhile the conventional linear regression method cannot obtain the standard deviation. Base on the reliability theory, a new method employing Solver add-in of spreadsheet was developed to calculate the shear strength parameters. The method was simplified by the principle that the shortest distance form origin point to the limit state surface in the normalization space was the reliability index. Four hundred and four samples of direct shear tests of rock mass from many large hydraulic projects in China were analyzed by four statistic methods including the new proposed one. Comparing results of different methods indicated that the new reliability statistic method had good performance than the traditional ways.