Abstract: In order to realize the dynamic uncertainty back analysis of rock and soil parameters along with the construction process, the multi output support vector machine method and Bayesian theory were introduced into the dynamic uncertainty back analysis of rock mass parameters. Aiming at the left bank slope of Baihetan Hydropower Station, we established a probability back analysis method of jointed rock mass parameters based on displacement and relaxation depth. The results showed that the proposed uncertainty back analysis method provided more information about geotechnical mechanical parameters, thus can further match the complexity and uncertainty characteristics of geological engineering, realizing dynamic updating of parameters and their uncertainty characteristics during the construction process. The proposed method is feasible and can be applied to similar projects.