Abstract: Inter-cropping with Ageratum conyzoides may effectively control major pathogens in citrus orchard. The research showed that flavones produced by and released from A. conyzoides could inhibit the major fungal pathogens,such as Elsimoe fawcetti Bit. Et Jenk, Collelotrichum gloeosporimdes Penz, Oidium tingitaninum Carter, Capondium citri Berk et Desm in citrus orchard. 10 flavones,including one glycoside,from A. conyzoides plant were isolated and identified. Most of them could gradually degraded in soil and only 3 flavones could be accumulated and last a long time. Just these 3 flavones could obviously possess inhibitory effect on fungal pathogens in citrus orchard. The inhibitory effect of the 3 flavones was stronger,not only than those of other allelochemicals produced by and released from A.conyzoides,but also than that of Carbenzin,a commercial fungicide. Therefore,the flavones produced by and released from A.conyzoides played an important role in pathogens control in citrus orchard.