Abstract: The deformation modulus of rock mass is an important parameter for evaluating the mechanical behavior of rock slopes. The deformation modulus of rock mass varies with the development and distribution of joints. Accurately estimating the deformation modulus of jointed rock mass is very important and is also one of the thorny problems in the field of rock mechanics. In this paper, the deformation modulus of jointed rock mass under confining pressure is studied by adopting the superposition principle(considering the deformation of intact rock and joints separately).Analytical methods for the deformation modulus of single joint and joint group are proposed for two jointed rock mass models: (a) the two ends of the joint intersect with the left and right sides of the rock mass and (b) the two ends of the joint intersect with the upper and left(or right) boundaries or the lower and right(or left) boundaries of the rock mass. Comparing with the results of the numerical simulation(finite element program), it can be seen that the error between the analytical calculation results of this paper and the numerical analysis results is small, basically less than 20%.The application of this method is further discussed, and it is proposed that the analytical method combined with the strength formula of jointed rock mass can obtain the deformation failure threshold of jointed rock mass, which can be used to predict and provide early warning for the deformation failure of the jointed rock mass. This analytical method provides a certain theoretical basis for the estimation of the deformation modulus of jointed rock mass.