NOVELTY - Method for utilizing water hyacinth plant and/or plant waste involves (a) planting water hyacinth, pressing, and collecting juice and residue, (b) mixing water hyacinth juice with e.g. antioxidant component to obtain plant nutritional liquid, (c) fermenting e.g. water hyacinth residue to obtain e.g. methane, (d) using methane to generate electricity, and incubating fermentation in greenhouse, (e) one portion of carbon dioxide is used in fermentation and another portion is transported to greenhouse, and (f) using residue as organic fertilizer for plant fertilization.    USE - The method is useful for utilizing water hyacinth plant and/or plant waste and preparing organic fertilizer (claimed).    ADVANTAGE - The method is environmentally-friendly, utilizes rapid growing plant as bioenergy material, does not waste gas, and water, discharges residual heat and waste into the process of circulating agricultural production.    DETAILED DESCRIPTION - Method for utilizing water hyacinth plant and/or plant waste involves (a) planting water hyacinth in polluted source of water, pressing water hyacinth plant, and collecting water hyacinth juice and residue, (b) uniformly mixing water hyacinth juice with cobalt amide, calcium nitrate tetrahydrate, antioxidant component and water to obtain plant nutritional liquid, where the antioxidant component is at least one chosen from 4-methoxyphenylacetic acid, 2-methyl-2-phenoxypropanoic acid, potassium sorbate, sodium benzoate and calcium propionate, (c) fermenting water hyacinth residue obtained in step (a), plant waste, livestock waste and fermented bacteria to obtain methane and carbon dioxide, (d) using methane to generate electricity or as fuel, where the electricity generated is used for greenhouse facility, and for living and working, the heat generated by electricity is used greenhouse production, and incubating fermentation step (c) in greenhouse, (e) one portion of carbon dioxide is used in fermentation, and another portion is transported to greenhouse, and (f) using the residue produced by fermenting as organic fertilizer for plant fertilization.