Abstract: Cultivating Rumex japonicus Houtt (picked from the shore of Shahu Lake around campus of HubeiUniversity) in sewageof Shahu Lake in order to observe the growth stateof them, the results showed that R. japonicus Houtt can give birth very well insewage, that every line of plant could bring about many fibrous roots which reached 01.3cmto 0.5cm in the first day and that thelongest fibrous roots reached about 23.5 cmduring 12 days. The experiment also showed that biggest plant of them could producedlargest biomass and the maximum evapotranspiration which get to 420ml per day and the total volume of evapotranspiration was1820ml during 12 days, But the smaller is R. japonicus Houtt, the bigger increased net biomass (daily increasing weight per g) ;Because of purification function of R. japonicus Houtt,the sewage became nealy clear and the transmissivity increased from 96 to99.1(while tap water is 100), namely more muddy sewagehad already turned into nearly transparent water. After determining thepollution index of sewage, it was the purification function of R. japonicus(No16) that COD of sewagewas changed from 49mg/Lto 28/L and its N-NH3from 328mg/L to 82mg/L, its P from 2.931mg/L to 0.062mg/L., In a word, All results indicated thatRumex japonicus Houtt is a kind of better plant fitting for sewage treatment.