Abstract: Effects of initial phosphorus concentration in water on growth and phosphorus uptake of Spirodela polyrrhiza was investigated through an aritificial culture experiment in laboratory.Results show that in the water with an initial phosphorus concentration being 3.0 mg·L^-1 Spirodela polyrrhiza grew and multiplied the fastest,maintaining the highest relative growth rate.The phosphorus removal rate reached beyond 70% when the initial phosphorus concentration in the solution ranged between 0.3 and 3.0 mg·L^-1.Both its cumulative phosphorus uptake and its phosphorus absorption rate increased with the increase in initial phosphorus concentration in water.However,drops began to appear in cumulative phosphorus uptake and phosphorus uptake per unit of mass of fresh Spirodela polyrrhiza when it grew in the water with an initial phosphorus concentration reaching 45.0 mg·L^-1.When the plant grew in water with an initial phosphorus concentration being lower 1.5 mg·L^-1,its ACPase activity increased,but its longer exposure to low phosphorus strees would narrow the difference in ACPase activity between treatments of low and high intial phosphorus concentrations.