The invention relates to a method for improving an eutrophic water body by planting vegetables on a water surface, which comprises the following steps of: (1) selecting fresh water of which the nitrogen content is more than or equal to 0.5 mg/L, phosphorus content is more than or equal to 0.05 mg/L and potassium content is more than or equal to 0.5 mg/L in a water body; (2) enclosing a vegetable planting area; (3) arranging the vegetable planting area; (4) manufacturing a floating planting bed; (5) selecting vegetable varieties; (6) planting vegetables; (7) managing, namely controlling the speed of water flow according to the growth vigor of the vegetables and a detection result of water quality, so that compared with a water inlet in the planting area, at a water outlet, the total nitrogen content is reduced by 30 to 90 percent, the total phosphorus content is reduced by 20 to 70 percent, and the potassium content is reduced by 10 to 50 percent while the growth vigor of the vegetables is ensured; and (8) selecting the vegetable varieties which is suitable to be planted in different seasons, and planting in turn throughout the year. In the method, the eutrophic water body is improved effectively by a biological cleaning method, and compared with physical and chemical means of managing the eutrophic water body, the method has obvious effect and low investment cost and is convenient to popularize and perform large-scale planting; and the vegetables are planted without applying fertilizer and spraying pesticides, so a new pollution source is not generated, and the planted vegetables reach the standard of green organic vegetables. By the method, resource utilization is maximized, and vegetable baskets of people are abundant while the eutrophic water body is managed. The production management and monitoring are convenient, so the method is particularly suitable for the large-scale planting.