Abstract: It is normal to get parameters of rock mass through tests in engineering. Due to consideration of randomicity and illegibility, random-fuzzy method is more reasonable than other usual methods. The core of conventional random-fuzzy method is reflecting the uncertainties by membership function. Though it does not eliminate the influence of mutation points, it decreases that in some extent. In this paper, based on statistics and criterions, the mutation points are chosen and deleted by a more reasonable method, which eliminates the points that have small membership degree. Then, this method is certified through a project.