Abstract: A survey was conducted with the square intercept method on species and quantity of weeds in 6 kinds of habitats where ragweed (Ambrosia artemisiifolia L.) grew in Hunan Province，the species richness index, diversity index and evenness index were analyzed. Results showed that a total of 83 indigenous species were collected and among them, 41 species were common indigenous plants, belonging to19 families. Invasion of ragweed caused significant (P < 0. 05 or P < 0. 01) decline of species richness index、Simpson index and Shannon-Wiener index and little change of Pielou evenness indexes in all the habitats involved. The variation in species richness index of ragweed invasion communities in the different season was small ，diversity indexes and evenness indexes were increased in spring and summer. It was suggested that the invasion of ragweed is harmful to biodiversity.