Abstract: The data mining techniques were used to predict shear strength of slip zone soil. In order to define the qualitative and quantitative factors affecting the shear strength, the CHAID (Chi-squared Automatic Interaction Detector) method and correlation analysis were used to pretreat data. According to the result obtained by CHAID method the landslides are classified by sedimentary environment of slip bed. Based on the classification, the influencing factors were selected in the light of Pearson correlation coefficient. The correlation analysis result shows that the internal friction angle of slip zone is affected by different factors as the slip bed of different sedimentary environment. The cohesive force has no obvious relationship with the factors. Stepwise regression was carried out to establish regression model for internal friction angle. The regression equations are passed statistical test and of good fitting degree and prediction accuracy. The forecast equations for the actual project data have good performances.