Abstract: In view of the large number of uncertainties in the inversion of mechanical parameters of concrete dam materials, the Markov chain Monte Carlo (MCMC) stochastic inversion method for elastic modulus of the dam body and deformation modulus of the dam foundation of the high concrete gravity dam is proposed. The deformation moduli of the dam body and dam foundation are considered as random variables. Based on the Bayesian theory, the Markov chain Monte Carlo without likelihoods method is used to sample the posterior distribution of the random parameters. The stationary Markov chain is used to obtain the random samples of the posterior distribution of parameters, and then the corresponding expected values and standard deviation are obtained. Taking the Longtan high concrete gravity dam as an example, based on the two-dimensional plane model for typical dam section, the deformation moduli of the dam body and foundation are inversed by the proposed method, and the distribution of the required inversion parameters (elastic modulus of the dam body and deformation modulus of the dam foundation) is obtained. The relationships between the statistical characteristics of the deformation modulus distribution of the dam body and foundation and the fluctuation of the observed values are analyzed. It is concluded that the variability of the posterior distribution is positively correlated with the discreteness of the observed values.