NOVELTY - A small annual composite purification system for purifying domestic sewage by water hyacinth comprises a buffer tank (1). An aeration tank (201), an anaerobic fermentation tank (202), a water hyacinth culture tank (301), a small constructed wetland (302) and a biogas tank (401) are arranged in a greenhouse (501). A heat supply network (502) is arranged below the greenhouse. Matrix of the small constructed wetland is limestone particles of 0.5-1 mm; and mater convolvulus is planted on it.    USE - A small annual composite purification system for purifying domestic sewage by water hyacinth.    ADVANTAGE - The system integrates the municipal sewage treatment, biogas production, phosphorus recovery, and the heating and thermal insulation system to solve problems of deep purification of municipal sewage, nutrient salt resource recovery, wetland plant treatment and recycling, and annual efficient operation of the system.    DETAILED DESCRIPTION - A small annual composite purification system for purifying domestic sewage by water hyacinth comprises a buffer tank (1). An aeration tank (201), an anaerobic fermentation tank (202), a water hyacinth culture tank (301), a small constructed wetland (302) and a biogas tank (401) are arranged in a greenhouse (501). A heat supply network (502) is arranged below the greenhouse. Matrix of the small constructed wetland is limestone particles of 0.5-1 mm; and mater convolvulus is planted on it. Sewage in the buffer tank is introduced to the aeration tank by a pipe network after regulating the pH. Precipitable substances and floating substances in the sewage are removed in the aeration tank, then, the sewage is fed to the anaerobic fermentation tank for performing anaerobic fermentation and denitrification. The sewage discharged from the anaerobic fermentation tank sequentially flows through the water hyacinth culture tank and the small constructed wetland for removing the phosphorus elements, nitrates and impurities in the sewage, then the sewage is discharged into a river network system. The water hyacinth in the water hyacinth culture tank and the mater convolvulus in the small constructed wetland are delivered into the biogas tank for fermentation. The biogas slurry produced in the biogas tank is fed to a phosphorus recovery module (6) containing lime and aluminum sulfate flocculant. The biogas produced in the biogas tank is fed to a hot water boiler (503). The hot water of the hot water boiler is fed to a heatsupply pipe network; and the heat produced by the heat supply pipe network is supplied to the greenhouse.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic diagram illustrating the small annual composite purification system.    Buffer tank (1)    Phosphorus recovery module (6)    Aeration tank (201)    Anaerobic fermentation tank (202)    Water hyacinth culture tank (301)    Small constructed wetland (302)    Biogas tank (401)    Greenhouse (501)    Hot water boiler (503)