Biological invasion is one of the most three critical environmental problems in the world. Biotas inwater system are always changing rapidly because of being weak at invasion resistant. In this paper, twotypical invasive plant species in water systems in Shanghai was discussed. (1) Eichhornia crassipes, infreshwater system, whose invasion process, invasion mechanism, harm, and control strategies were elu-cidated; (2) Spartina alterniflora, in estuarine water system, whose transplanting in Chongming EastBeach of Shanghai causes large controversy, was recognized as a critical invasive species. The currentidea for these two plant species and some suggestions on study and control of biological invasion werediscussed.