The invention discloses a method for removing or inhibiting alga in eutrophic water. The method is characterized in that clay and clayey soil are taken as primary raw materials to produce ceramsite, and the ceramsite is pre-processed; the pre-processed ceramsite is produced into phosphorous removal modified ceramsite and iron removal modified ceramsite; the phosphorous removal modified ceramsite and the iron removal modified ceramsite are filled into an alga removing device; the alga removing device is transported to the place where algal bloom takes place, the alga removing device in water issalvaged after soaking is conducted for 5-7 days, and the modified ceramsite which completely absorbed alga is poured out. The method has the advantages that on one hand sunlight can be shaded usingthe alga removing device so that the alga in the water cannot perform photosynthesis to inhibit the growth of the alga, on the other hand, the growth of alga cells is inhibited due to limited nutrients, the modified ceramsite which completely absorbed the alga can be used for producing fertilizers for potted flowers, the generation of rubbish is avoided, and resources are recycled, which is more environmentally friendly.