Abstract: In order to get the equivalent cohesion C and the friction angle φ of the rock mass conveniently, the paper used generalized Hoek-Brown failure criterion and RMR method of rock mass quality classification to calculate the C and φ with the different RMR, and fit the reduction factor of C and φ with RMR curve. The result shows that the reduction factor of C and φ can be calculated according to RMR while the rock mass quality classification is fairly good. The known C and φ of rock was reduced to obtain the C and φ of the rock mass. The C of the rock mass is positively linear related to uniaxial compressive rock strength, and the φ of rock mass is unchanged with the different uniaxial compressive rock strength. The reduction factors of C and φ are unchanged with the different uniaxial compressive rock strength, only concerned with the RMR.