Abstract: To investigate effects of residual aluminum flocculant on the growth of submerged macrophyte Potamogeton crispus and water quality of the West Lake diversion project, the method of outdoor simulation was utilized with four different treatment groups: the control group (no addition), low-dose group (35050) g/L, middle-dose group (65070) g/L and high-dose group (1100150) g/L. The results showed that: (1) high-dose addition increased significantly the concentration of aluminum salt in water, while low and medium-dose addition had little effect. (2) The concentration of aluminum salt in water increased first then decreased latterly and pH had a little change conversely, and total phosphorus decreased accordingly; Total nitrogen, phytoplankton density and turbidity in water of every group had a clear decline. (3) Three treatment groups of P. crispus had almost no significant changes in the biochemical indi-cators compared with the control group. On experimental concentration of alum flocculant dosing, P. crispus was growing with no obvious damage, and the concentration was in the tolerance range of P. crispus. Hence we suggest that P. crispus can be selected planting near the water inlet districts of diversion project for submerged macrophyte restoration in West Lake, Hangzhou.