Abstract：There are various methods for evaluating engineering quality of rock masses，and indexes for different methods are different. Those different factors or indexes in different methods cannot be employed together due to the difference in the evaluation standard of different methods. This leads to the limitation of the traditional evaluation method. Based on extenics，a quantitative evaluation model of rock mass quality of multiple parameters is developed. The advantage of this model is that different factors from different traditional evaluation methods can be considered simultaneously. For example，the factor RQD in RMR can not be used together with the factor Jr in Q system previously because of differences in evaluation standard. But through linear dimensionless method，factors are converted to dimensionless numbers，so those two factors can be used together. Based on the concept of degree of membership and extenics，different factors from different traditional methods are selected and converted to dimensionless numbers. A quantitative method for define the weight of those factors are put forward according to importance of factors. The results of a case show that this evaluation method is feasible.
