The invention discloses a method for growing watermelons by using flue-cured tobacco seedling growing greenhouse seedling growing raffinate. The method comprises the steps of retaining nutrient solution after flue-cured tobacco floating seedling growing, placing cultivation frames in a seedling growing tank at intervals, filling the cultivation frames with nutrient soil above the water level of the nutrient solution, transplanting cultivated watermelon seedlings in the nutrient soil in May, inserting pulling rods in the cultivation frames to pull watermelon vines to sunshade net racks to meetneeds of development space and sunlight required for the growth of the watermelons, and managing according to conventional watermelon cultivation. According to the method, floating seedling growing nutrient solution is used for cultivating the watermelons, wastes are turned into treasures, and the method avoids causing the drawback of surrounding water body pollution such as eutrophication causedby direct discharging, thereby avoiding resource waste and avoiding the environment problem of surrounding water body pollution.