Abstract: Through the comparison and analysis of the relevant contents of the new and old NS(National Standard) standards of engineering classification of rock masses(GB 50218-94, GB/T 50218-2014), the improvement of the new national standard was pointed out. Based on the national standard of engineering classification of rock masses (GB/T 50218-2014), the simplified calculation method of BQ has been put forward, and the relationship figure has been plotted between basic quality index of rock mass and rock integrity coefficient. The relationship table is established among BQ and R_c and K_v. Through the combination of the chart and the table, it can determine the basic quality of rock mass grade faster. It is concluded that it could provide reference for the stability analysis of underground engineering.