Acorus calamus Linn. has been selected as the experimental plant, and the variation of its aerenchyma and the quantity of its radial oxygen loss (ROL) under the stress of three different concentrations of nitrogen and phosphorus effluent (Group 1:N 40 mg/L, P 4 mg/L; Group 2:N 80 mg/L, P 8 mg/L; Group 3:N 120 mg/L, P 12 mg/L) in the water culture has been investigated. The results show that the stress of high concentrations of nitrogen and phosphorus significantly inhibited the growth of root length and plant height of Acorus calamus Linn. and reduced the number of plant roots; it could also increase the quantity of ROL and promote the formation of aerenchyma. The gross quantity of ROL in the stress group was less than that in the control group due to the decrease of root length and quantity. The ROL trend has not changed by the stress of high concentrations of nitrogen and phosphorus, and the further distance away from the roots, the smaller quantity of the ROL. This research also found that the amount of the root tip's ROL showed positive correlation with aerenchyma while the amount of ROL of basal zone and mature zone showed insignificant correlation with the aerenchyma.