Abstract:Taking a long sequence test data of shear strength of quaternary clinosol and residual cohesive soil in shallow-buried tunnel section as a base,the authors studied the probability distribution of the parameters and fitted their probability density function by check method and finite contrast method,used Bayes method to optimize cohesion and internal friction angle of a soil tunnel,and discussed the relation of the probability distribution and variation factor. The research results show that optimum probability distribution of the cohesion is normal distribution,but the internal friction angle¢s is logarithm normal distribution. Extreme type I isn¢t equal to be probability distribution of cohesion and internal friction angle of clinosol and residual cohesive soil surrounding rock. When variation factor is lower,optimum probability distribution,normal and Bata distribution have little influenc on the internal friction angle,but whenever optimum probability distribution is best choice for cohesion. Variation factors of cohesion and internal friction angle minish and the data are more reasonable after they are optimized through Bayes method.