Abstract: The aquatic plants in Changhu Lake were investigated on January, April, and July and October 2015, the seasonal changes of dominant species, species diversity, and niche width and overlap value of aquatic plants in Changhu Lake were analyzed. The first three important species in winter and spring were Potamogeton crispus (the submerged plant), P. maackianus (the submerged plant) and Typha angustifolia (the water plant). The relatively important value of Nymphoides peltatum (the floating leaf plant) and Eichhornia crassipes (the floating plant) were increased in summer and autumn. The Shannon-Wiener index (H’) and Simpson index (D) were used to evaluate the diversity of aquatic plant in Changhu Lake. The results showed the highest diversity index (H’=2.946 and D=0.940) in summer and the lowest diversity index (H’=0.931 and D=0.428) in winter. The niche widths of the dominant species P. crispus were 0.523 in winter, 0.363 in spring and 0.273 in summer, respectively. The niche widths of other species were less than 0.2. The aquatic plants in Changhu Lake tended to specialized species. In addition, there were also a few species with niche overlap, with 7 pairs in winter, 19 pairs in spring, 23 pairs in summer and 17 pairs in autumn. The species with similar ecological habit and ecological requirements showed the higher niche overlap index, such as between the submerged plants of Hydrilla verticillata and P.malaianus, the floating plants of Azolla imbricate and Salvinia natans, the water plants of Polygonum orientale and P. hydropiper, Myriophyllum spicatum (the submerged plant) and Trapa bispinosa (the floating leaf plant). There was more niche overlap between the dominant specie P. crispus and the other species, 4 pairs in winter and 9 pairs in spring and 7 pairs in summer and only 1 pair in autumn. The ecological niche could better explain the species composition, distribution characteristics and diversity changes of aquatic plants in Changhu Lake. The results showed that the composition of aquatic plant species was simple and the stability of population structure was poor in Changhu Lake.