Abstract：The importance of study on mechanical parameters of rock mass，and some methods to determine mechanical parameters of rock mass are introduced. Hoek-Brown strength criteria is considered as the authoritative method to get rock mass mechanical parameters from rock mechanical parameters which are got from laboratory. While Hoek-Brown criterion does not give the calculation expressions for rock mass between disturbed and undisturbed. Zhang Jianhai finds this shortcoming and gives his modified expressions，however，only simple average treatment for Hoek-Brown criterion，and the disturbed degree of rock mass can not be described in his modified expressions. H. Sonmez and R. U1usay consider the disturbed degree of rock mass and give their modified expressions，the shortcoming of Hoek-Brown strength criterion and above modified expressions of which are pointed out；and the modificatory coefficients Km，Ks which can take the degree of disturbed rock mass into account are constituted；then the modified expressions for Hoek-Brown strength criteria are brought forward. Km，Ks are based on integrality coefficient Kv，so they can not only reflect the distributed degree of rock mass，but also be got easily. The shortcomings of Hoek-Brown criterion and its former modified expressions are overcome. The modified expressions can determine the mechanical parameters of rock mass between disturbed and undisturbed better. The calculation is carried out through the modified expressions and other methods，respectively，where the study on mechanical parameters of rock mass from Changba Lead-zinc Mine. It is found that the modified expressions in this paper is more suitable to determine the mechanical parameters of rock mass between disturbed and undisturbed；and the result form this method is closer to the measured one. Based on comparative study，the rationality of these modified expressions is further explained.
