Abstract: The discovery,synthesis,fungicidal activity,toxicological properties of(E)-methyl 2-［2- (3-n-butyl-4-methyl-2-oxo-chromen-7-yloxy) methyl phenyl］-3-methoxyacrylate(coumoxystrobin,SYP-3375) were introduced.Coumoxystrobin was synthesized from ethyl acetoacetate as starting material via several steps including alkylation,cyclization and condensation.The structures of coumoxystrobin and the intermediates were identified by nuclear magnetic resonance(1H NMR),IR and elemental analysis.The bioactivity results showed that in greenhouse conditions coumoxystrobin had lower activity in controlling cucumber downy mildew and powdery mildew than contrasts,in field trials,the fungicidal activity against cucumber downy mildew of coumoxystrobin at 100 g(a.i)/ha was almost equivalent to that of enestroburin and azoxystrobin,the fungicidal activity against cucumber powdery mildew at 50 and 200 g (a.i)/ha was lower or equivalent to that of enestroburin EC.