With the urbanization construction in Leshan extends to the shallow hilly region, the wide distribution of quaternary silty clay has become geological background of engineering construction. The quaternary silty clay can be divided into three types according to its characteristics of engineering geology, including the perennial water saturated zone gully slope alluvial silty clay (type A), the seasonal water saturated zone gully slope alluvial silty clay (type B) and silty clay of slope area (type C), and the variation of partial physical and mechanical parameters have been compared and studied; Based on χ^2 goodness of fit test and reliability probabilistic truncation, the author established shallow hilly area clay probability density function and the optimal probability distribution model, and gave recommended range of all kinds of physical and mechanical parameters. The result shows that: (1) the variation of mechanical parameters of silty clay parameters > physical parameters, different types of silty clay parameter variability, type A> type B> type C; (2) The optimal distribution model of physical parameters is normal distribution, and the optimal distribution model of the mechanical parameters is mostly logarithmic normal distribution; (3) Compared with different kinds of silty clay, the optimal distribution model of type B and type C silty clay parameters are mostly normal distribution, and the optimal model of type A silty clay parameter is log-normal distribution. Taking the P=0.683 as the sample parameter reliability truncation probability, the proposed value range of silty clay parameters in Leshan shallow hilly region is given, which provides a scientific basis for reliability design of geotechnical engineering in this area.