Abstract: Eupatorium catarium Veldkamp, an agressive plant, has spread througout the agroecosytem and wilderness in Hainan and Guangdong province in the last decade and has become a serious problem in many parts of this area. Preliminary research on the Allelopathy of this species found that the aquous extract has strong inhibition to the seed germination and seedling elongation of cabbage and radish. In present study the allelopathy of this species to five conmon weeds (E. odoratum L., Mimosa pudica L., Echinochloa crusgalli (L.) Beauv, Bidens pilosa L. and Abutilon theophrasti Medic) in south China was investigated to further understand its allelochemical potential and the potential used as green manure in cropping system weeds management. Two kinds of aquous extracts, one from fresh matieral and another from dried material, were compared. The result indicated that two kinds of extracts both have strong inhibite effect on five weeds. The roots of five species all showed more sensitive to the extracts than seeds. Under higher extracts density, the roots were inhibited completely. For different species, M. pudica had strongest endurance to the extracts, E. odoratum followed it. There was no siginificant disciplinary differences between two extracts. The results suggested that E. catarium has the potential to be used as green manure in cropping system weeds management, but enough researches need to be conducted to well use it in different systems.