NOVELTY - A composite man-made ecological floating island comprises algae-bacteria biofilm carrier units flexibly connected with sludge ecological floating island units comprising (wt.%) sludge powder (60-77), light material (3.6-8), coagulated cured material of inorganic binder (19.4-32) and water. The biofilm carrier units comprise algae-bacteria biofilm adhered to a surface of porous high molecular light suspended carrier. The floating island units are flexibly connected through sponge or polystyrene foam.    USE - Composite man-made ecological floating island.    ADVANTAGE - The floating island has widely available raw materials and stable chemical properties; is low cost and environmental friendly; has no secondary pollution; utilizes waste sludge in sewage treatment plant, thus reducing municipal sludge; and recycles waste resource. The floating island can be planted with water purifying plants, thus forming microecological community with microorganisms for purifying polluted water body, and providing better water purifying effect compared to conventional floating island.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for constructing the composite man-made ecological floating island comprising:    (A) conducting innocent treatment to waste sludge of sewage treatment plant to obtain sludge powder, light material and inorganic binder;    (B) manufacturing mold by rigid material, and adding water to uniformly mix sludge powders, light material and inorganic binder;    (C) filling uniformly stirred mixture into mold, tightly pressing and compacting, and inserting metallic hooks into mixture at fixed points, where metallic hooks are fixed after mixture is cured, dried and molded;    (D) removing mold to obtain finished product of sludge ecological floating island unit;    (E) using porous high molecular light suspended carrier as phycomycete biological membrane carrier;    (F) cutting porous high molecular light suspended carrier, and fixedly equipping rope shaped flexible material at one end of carrier and bag shaped flexible material at other end of the carrier;    (G) culturing water purifying algae in large size culturing box by a culture medium, placing the cut porous high molecular light suspended carrier into the culturing box;    (H) suspending carrier in culture liquid in the box as carrier, and culturing for 6-10 days, where the appearance of bubble on carrier marks the formation of the algae membrane on the carrier unit; and    (I) firmly tying rope shaped flexible material at one end of the phycomycete biological membrane carrier on metallic hook at bottom of the sludge floating island so that the phycomycete biological membrane carrier unit is flexibly connected with the sludge floating island unit, where large size floating island is formed by connecting floating island units, which are flexibly connected by sponges or polystyrene foamed materials.