The invention relates to an application of a phenazine-1-carboxamide modified compound 18-3 in the inhibition of Sclerotinia sclerotiorum. The phenazine-1-carboxamide modified compound 18-3 is obtained through structure modification of phenazine-1-carboxamide used as a parent substance. The inhibition effect of the modified compound 18-3 on the Sclerotinia sclerotiorum is detected through adopting a growth rate technology, and a result shows that the modified compound 18-3 has an inhibitory effect on the strawberry gray mold, and has a higher Sclerotinia sclerotiorum inhibition effect than the parent substance phenazine-1-carboxamide, so the modified compound 18-3 can be used as a lead compound of new pesticides for controlling the Sclerotinia sclerotiorum.