Abstract: By means of collecting specimen in fields, examining specimen in herbaria and researching literatures concerned, the floristic interrelationship of aquatic plants between Northeast China and some relational regions was primarily analysed. As Japan was once joined with the continent of Eurasia in ice-age and now the climate close to that of Northeast china, the coefficient of similarity of aquatic plants from these two regions is found to be the highest. During the Pleistocene,most species of aquatic plants were exchanged from Northeast China to the Far East region when Ancient Nen-Lao River linked to Zeja River and some relic species of the Teriary Period were preserved in both the regions. A little tepid species, however, couldn't be distributed from Northeast China to the Far Eastregion, the coefficient of similarity from these two regions is therefore somewhatlower. Indian-Subcontinent. Australia. Southeast Asia and Africa show the Lowest similarity coefficient of aquatic plants for where the climates are obviously different from that of Northeast China. Of all the internal areas compared, the highest coefficient of similarity is shown by the plants from North China because NorthChina and Northeast China are, not only contiguous together but the rivers scattered over the two areas were all belong to the hydrographic net of Ancient Yellow River. On the contrary, aquatic plants from Hainan showed the lowest coefficient for the Island is geographically isolated from Northeast China.

Key words: Northeast China, Flora of aquatic plants, Relational region, Coefficient of similarity