Water parsley(Oenanthe javanica(Blume) DC) was raised with varying population density(S) in the laboratory aquarium unit to determine the growth equation. The population density was measure after 7 days. The resultant growth curve was well fit to the equation 1/S = A+B (1/S0) with a high correlation coefficient ($R^2$ = 0.999). The maximum specific absorption rate was $9.011 imes 10^{-5}$ kg $NO_x-N/kg$ water parsley$cdot$day and $1.31 imes 10^{-5}$ kg $PO_4-P/kg$ water parsley$cdot$day when the average population density was $2.62 kg/m^2$. The relationship between population density and nutrient absorption rate, the absorption rate of $NO_x-N$ was 5.04~5.24 mg/l$cdot$day when the population density was $7.51~10.0 $mg/m^2cdot day$ and the absorption rate of $PO_4-P$ was 0.56~0.78 mg/l$cdot$day when the population density was 5.02~10.0 $</TEX>kg/m^2cdot day$. Taking into account the nutrient absorption rate and growth rate, the population density between $7.0 kg/m^2cdot day$ and $8.0 kg/m^2 cdot day$ was selected. The removal rate of nutrient was investigated after 7 days culture. Removal rate of $NO_x-N$ was 95.6~99.95% with initial concentration of 35 mg $</TEX>NO_x-N/l$, and the removal rate of $PO_4-P$ was also high, indicating 80.24~98.9% with initial concentration of 5.95 mg $PO_x-P/l$.