【Aim】 To clarify the effects of Bidens alba invasion on the composition and species diversity of plant communities. 【Method】 The plant species, coverage, height, and density in communities of B. alba (experimental plot) and no B. alba (control plot) were investigated in Maoming, Guangdong Province, China. The important values and diversity indices of different plants were calculated. The Pearson correlation coefficient and fitting curve were used to show the relationship between the characteristics of the B. alba population and its important values and species diversity. 【Result】 The composition and structure of the plant community changed significantly after the invasion of B. alba. The number of species decreased from 104 in the control plot to 63 in the experimental plot. Some species, such as Paspalum distichum, Hedyotis diffusa, and Cuphea balsamona, disappeared. The important values of malignant weeds, such as Ageratum conyzoides, Spermacoce alata, and Praxelis clematidea, decreased, while those of Digitaria sanguinalis, Mikania micrantha, and Alternanthera philoxeroides increased. The Patrick richness index (R), Simpson's diversity index (D), and the Shannon-Wiener diversity index (H) values of the experimental plot were all lower than those of the control plot. The important values of B. alba were negatively correlated with the above diversity indices (H, D) and richness index (R) (P<0.001). 【Conclusion】 The invasion of B. alba significantly changed the structure and reduced the species diversity of plant communities. The harm caused by B. alba to the ecological environment in southern China is worthy of attention.