Abstract: Now damage mechanics is regarded to be an effective tool to study the mechanical behavior of jointed rock mass. However, the joint geometrical characteristic is only considered in the definition of most current jointed rock mass damage variables without considering the joint mechanical parameters such as joint internal friction angle, which obviously cannot reflect the mechanical property of jointed rock mass. So, a damage variable (tensor) comprehensively considering the joint geometrical and mechanical parameters is deduced, from which a damage constitutive model for rock mass under uniaxial compression load is set up. Therefore, the damage variable calculation formula of the rock mass with a non-persistent joint is firstly deduced based on the connection of the increment of additional strain energy caused by the existence of one joint in fracture mechanics and the emission of damaged strain energy in damage mechanics. Secondly, the calculation method of the stress intensity factor of a single joint under uniaxial compression is studied according to fracture mechanics theory, and the calculation formulas of the stress intensity factor K_Ⅰ and K_Ⅱ are obtained. Finally, this model is adopted to calculate the climax strength and damage variable of rock mass with a single non-persistent joint under uniaxial compression load. The results show that the rock mass strength is the same as that of the intact rock and the damage is zero when the joint dip is less than its internal friction angle. Then with increase in joint dip, the change laws of rock mass strength and damage with the joint dip are parabola with the hatch up and down respectively. And the rock mass strength is least and its damage is largest when the joint dip is about 60°. With increase in joint length, the rock mass damage increases, while with increase in joint internal friction angle, the rock mass damage decreases.