Abstract: Using the object-oriented software, PowerBuilder, and DLL theory, an object-oriented back analysis method was studied, which defined the relationship of object classes, established a message flow of the finite element and made a program of friendly interface and efficient operation. With the applications of the probability theory and the mathematical statistics principle, the objects function of the geomechanical engineering random back analysis was established based on the AIC criterion of the decision information theory and the maximum entropy criterion, and an expanded Bayes method was thus proposed to overcome shortcoming of the conventional Bayes method. The models and analytical methods presented in this paper were verified by some numerical examples.