Abstract: Lake Honghu, which covers an area of 344.4 km² and has its center at 29°49' N, 113°17'E, is the biggest lake at Jianghan Plain, and a good representative of the lakes in the middle and lower reaches of Changjiang River.Different definations of aquatic plant are discussed.The aquatic vascular flora in Lake Honghu comprises 123 taxa, belonging to 36 families and 67 genera.The subtropical character of the flora in the lake is quite obvious.Flora similarities of the lake and other 11 ones are compared on the same ground.The geographic position, shape of lake basin, physical and chemical environment, climate and lake history all affect the flora similarities.No obvious change is found about the flora in the lake during the past 40 years.