Abstract:The effects of plant preservatives （Macleaya cordata extract）on the antimicrobial activity of postharvest pathogens in citrus fruits were discussed.Taking pathogenic fungi of green mold（penicillium digitatum）of citrus reticulate from shimen，changde，hunan and Chinese herbal medicine Macleaya cordata as test materials and bacteriostatic circle diameter as measurement index，the extraction conditions of antibacterial active substances and the antimicrobial stability of active substances were determined.The results showed that the extracts had strong bacteriostatic activity when 80 % ethanol was used as extraction solvent，the optimum extraction process conditions were as follows：the ratio of material to liquid was 1∶27.5（g/mL），ultrasonic extraction time was 2.5 h，extraction temperature was 72.5 ℃，ultrasonic power was 850 W.Under these conditions，the diameter of bacteriostatic circle was more than 30 mm，its bacteriostatic ability had been greatly improved compared with the extracts under other conditions.Ultraviolet irradiation for more than 48 h，alkaline environment，and Ag+，Fe3+，Cu2+metal ions，all of them had certain negative effects on the activity of extracts，the diameter of bacteriostatic ring was reduced by more than 20%.Storage for about 80 days at less than 20 ℃had little effect on the activity of the extract.