Without comprehensive consideration of the strength parameters statistical properties, the slope reliability index calculation value become smaller and the failure probability become larger, often more than 10%, which was difficult to adopt in design.Hence, the foundation reliability norm’s formulate and implement made slow progress. Take a completely weathered granite soil slope of an expressway as engineering background, and based on the analysis of the statistical characteristics of soil parameters, the limit equilibrium theory and monte carlo simulation method were used to systematically analyze the soil strength parameters’ mean uncertainty, variability, correlation and interval characteristics and spatial variability of impact on the reliability of the slope stability. The results showed that all kinds of statistical features of soil parameters had varying degrees impact on slope stability reliability. The reliability index calculation value increased with the decrease of the sampling distance, increased with the increase of the mean values of c or φ, decreased with the increase of the variation coefficientc and φ, increased with the increase of the correlation coefficient absolute value of c and φ, and the reliability index calculation value became obvious bigger when interval characteristics were considered. The findings indicated that variability was adverse to the slope stability and the correlation, interval characteristics and spatial variability were good for the slope stability. Therefore, with accurate and comprehensive consideration of the soil parameters statistical features, especially with the consideration of space variability and interval characteristics on the basis of the consideration of parameters variability and correlation will be more in line with the engineering practice, and the calculation results tend to be more reliable. It is advantageous to the adopt reliability norm and safety evaluation of slope engineering.