Twenty-three kinds of 8-substituded coumarins were synthesized by Perkin reaction and Knoevenagel reaction from 2-hydroxy-3-substituted benzaldehyde in yields of 66.2%-97.6%.The structures of the title compounds were characterized by FT-IR, 1H NMR, MS and elemental analysis.Their antifungal activities against mycelium growth of Botrytis cinerea, Citrusanthrax bacteria, Fusarium oxysporium and Valsa mali were measured.The results indicated that most of these compounds exhibited moderate to high antifungal activity.8-isopropyl coumarin showed strong fungi inhibition with EC50 of 21.74 and 27.14 mg/L against V.mall and C.bacteria respectively.The structure-activity relationship (SAR) showed that antifungal activity was enhanced when alkyl, aryl or halogen was introduced to C-8 of coumarin, while carboxylate, acetyl or phenyl on C-3 was detrimental to the antifungal activity.