The present invention belongs to the technical field of pesticides, and involves more specifically a substituted benzonitril diketone compound or a tautomer, a salt thereof, a preparation method therefor, a herbicide, and an application thereof. The substituted benzonitril diketone compound or the tautomer thereof and the salt thereof are as shown in the general formula I-1: R1R2N represents a formula (II), wherein R represents a formula (III). The obtained drug active substance exhibits a higher medical activity, a broader spectrum of activity, and improved drug safety.