Abstract: Based on the theory of displacement back analysis and the theory of geometrical damage, identification of damage parameters in joint rock mass is studied in this paper. The identification reliability of different parameters is discussed respectively according to the different number of crack group contained in the rock mass. Then the parameter combinations with high accuracy are obtained. For the cases in which the initial values have great effect on the accuracy of the result, Monte Carlo method is used to optimize the initial values,and the result shows that identification precision is improved greatly.