The surrounding rock quality and construction method are essential reasons affecting overbreak-underbreak of tunnels. It is important to evaluate and forecast overbreak-underbreak

and judge the stability of tunnel structure for researching the relation between surrounding rock quality and overbreak-underbreak. Based on the measured data and numerical experiment

the effect of span on surrounding rock quality is studied; and modified rock quality index based on multifactor evaluation is established. According to excavation section profile showing the fractal characteristics

the fractal dimensions of 20 sections profile of Yuanyanghui tunnel are calculated; and the relation between surrounding rock quality and overbreak-underbreak is studied. The linear relations among modified rock quality index and percent of overbreak and fractal dimension are gained. With the increase of modified rock quality index

the percent of overbreak and fractal dimension are decreased. According to the principle of multiple correlation

the multiple correlation among modified rock quality index and percent of overbreak and fractal dimension of section profile are established so as to provide reference for correct evaluation of surrounding rock quality and analysis of overbreak-underbreak. Meanwhile

by contrast with relation between different surrounding rock classifications and overbreak-underbreak

it is shown that BQ method based on multifactor evaluation has better adaptability in tunneling engineering.