Abstract: The inhibition activity on mycelium growth of 5 cationic surfactants and 3 fungicides against Sclerotinia sclerotiorum(Lib.)de Bary were determined by mycelium growth rate method in lab.And their effects on the pathogen' s mycelium shape,sclerotium formation,sclerotium germination,dry weight of mycelium and membrane osmotic potential were also studied.The results showed that dodecyl dimethyl benzyl ammonium chloride had the strongest inhibitory effect on mycelia growth,its EC50 value was 3.92 μg/mL,which was similar with fungicide diethofencarb.After treated with cationic surfactants,the mycelia became stout and had moniliform appearance.As the concentration of the cationic surfactants increased,the inhibitory effect on the growth and the dry weight of mycelium became stronger,and the mycelium's dry weight reduced more than 90%.And the sclerotium numbers decreased compared with that of the control,however the weight increased slightly.In contrast,after treatment with procymidone,the sclerotium numbers had no visible change but the weight decreased greatly.The 5 cationic surfactants even at the concentration of 10 000 μg/mL could not restrain the sclerotium germination completely,but the fungicides of procymidone and pyrimethaml could restrain it at the concentration of 200 μg/mL.