Based on the mild,moderate and severe communities of Eupatorium adenophorum,the structure,species composition and diversity of the plant community in the abandoned arable land of Dechang county,Sichuan province was investigated comparing with the structure characteristics of Eupatorium adenophorum.The results showed that in mildly occurred sites,the internal diversity index of this plant community varied slightly from 0.550 1 to 0.683 3; in moderately occurred sites,that decreased from 0.639 3 to 0.333 5; in the severe sites,Eupatorium adenophorum formed a regional communitygifted.The spreading of Eupatorium adenophorum in mild growth sites was relatively slow,the community was distributed fascicularly and sporadically,the density increased from 3 stems/m2 to 8 stems/m2 after a year,the coverage expanded from less than 5％ to near 10％; The density of Eupatorium adenophorum in moderate sites increased from 32 stems/m2 to 103 stems/m2 in the following year and the coverage expended from less than 35％ to more than 90％; the coverage,density and height of Eupatorium adenophorum in severe sites reached to the maximum,and accompanying plants were quite rare in the same period.