Abstract: The grading method is very important in the safety supervision and administration of major dangerous chemical hazard installations. Through a comparative study on three common methods used to grade major dangerous chemical hazard installations, a new grading method is proposed in which R is a grading indicator. In this method, R is calculated by the ratios of different chemical quantities and their threshold quantities in the unit after correction of chemical categories and numbers of people. This method is applied in one enterprise and the results show that it has a certain degree of science and better operability, and can meet the need of the grading for major dangerous chemical hazard installations.