The invention relates to a construction safety 5-parameter decision method of a tunnel drilling and blasting method. The decision method of the invention is realized in a way that the decision indicators comprise displacement value range, deformation rate range, deformation acceleration, crack support state and groundwater state; the decided danger classes, 18 status categories and the like are listed in Table 1; the corresponding construction measures are listed in Table 2; the invention also provides monitoring deformation displacement value, deformation rate value, deformation acceleration value and deformation time, which are carried out on the monitored cross section by using the drilling and blasting method with a total station and the like, crack state which is determined by using a crack width measuring and detecting instrument and the like, or groundwater state which is observed or measured; and according to Table 1, the current danger class of a certain cross section is determined, and the 5-parameter method is used for carrying out the decision. Compared with the prior single parameter method, the invention considers the geologic conditions, support parameters, construction methods, cross section dimensions, forms and other influential factors, thereby enhancing the accuracy and the universality; and the invention can forecast the safety of the tunnel comprehensively, truly and reliably.