Determining mechanical parameters of rock masses correctly is still a big problem over the years. A new method using fracture tensors to determine mechanical parameters of rock masses is presented considering the characteristics of the structures of rock mass. That is, joints were measured in situ and statistically analyzed firstly, then, three-dimensional joints network model was built, the fracture tensors and mechanical parameters were calculated in different dimensions of rock mass models; at last, the relationship between fracture tensors and mechanical parameters of rock mass was established. Therefore, the rock mass strength and deformability parameters can be estimated in any given direction from a single power function without performing expensive and time-consuming in situ tests, as long as the intact rock and the joint properties from laboratory or field tests and the joint geometry system from field joint mapping are known. The results will be useful for evaluating the stability of jointed rock engineering.