Abstract: Plant diversities of three Kosteletzkya virginica plantations, different in history (1, 2 and 5 years) in Qingkou Saltern of Lianyungang, Jinhai Farm of Yancheng, and Xiaoyangkou Salt Flat of Nantong, separately, and control plots (without K. virginica), one for each, were investigated using the typical quadrat method. Results show that the three plantations had 10, 7, and 9 species of plants, separately, and obviously all more than their respective controls. The controlswhich were dominated by Suaeda glauca and Phragmites australis, forming a mono-type of vegetation;The IVs (importance value) of K. virginica in the three sites were all over 0.6. The IV of S. glauca, P. australis and Aster tataricus in the Jinhai Plantation was 0.225, 0.272, and 0.199, respectively, that of Erigeron annuus and Setaria viridis in the Xiaoyangkou Plantation was 0.228 and 0.241 respectively, and that of S. glauca and Sesbania cannabina in the Qingkou Plantation was 0.433 and 0.332, respectively. In the controls, S. glauca and P. australis were the dominant species, all exceeding 0.6 in total IV of the two. The three plantations did not differ much from their respective controls in fresh plant biomass statistically, but the Jinhai Plantation and the Xiaoyangkou Plantation did in plant dry weight, indicating that the plants in the controls contained more water;. Furthermore, the three plantations were all higher than their respective controls in Berger-Parker richnesss index, Shannon-Wiener index, Simpson diversity index and evenness index, indicating that in the K. virginica plantations, the native species of plants can grow well in synbiosis with K. virginica, thus improving plant diversity of the coastal saline lands of Jiangsu Province.