Herein,the ethanol-extracts from 11 Chinese herbs were screened for their antifungal activities against Penicillium italicum. The extract from Ramulus cinnamomi showed the best antifungal activity against P. italicum and was chosen to study the antifungal mechanism. The spore germination,cell membrane permeability,mycelium morphology and mycelia inclusion contents were used to explain its potential mechanism. The results suggested that the ethanol extracts of R. cinnamomi,Cinnamomum japonicum and Cortex phellodendri showed good antifungal effects and their inhibition zones were all over 30 mm. Moreover,R. cinnamomi showed the best antifungal activity in all 11 herbs and was better than Bellkute( a chemical fungicide used in Citrus Postharvest Disease). The inhibition zone of R. cinnamomi was 34. 57 ± 0. 78 mm,meanwhile,the minimum inhibitory concentration( MIC) and the minimum fungicidal( MFC) concentrations were 3. 125 mg / mL and 6. 25 mg / mL,respectively. In addition,the antifungal mechanism suggested that R. cinnamomi extracts had interference effect on spore germination,mycelial growth and development,because it could effectively inhibit spore germination and damage the normal structure and stability of cell membrane. The increased permeability of cell membrane led to exosmose of mycelial contents,and then affected the growth and metabolism of mycelium. Ethanol-extract from R. cinnamomi showed good antifungal activity against citrus blue mould and thus could be used as a source of natural fungicides.