A method for harnessing, recovering and utilizing ecological farm is carried out by centrifugalizing out marsh slag and marsh liquid from marsh gas in livestock and fowls farm, sterilizing for marsh liquid, filtering by water, selecting chlorellin algae, expanding while culturing, raising fish and algae, inspecting while preventing pest diseases, collecting, recovering clear liquor, utilizing by livestock and fowls farm, extracting algae mud from algae liquor, mixing with feed, returning farm for animals and fowls, inoculating while fermenting, mixing fermented algae bacterium nutritive liquid with feed for animals and fowls, or extracting algae mud from algae liquor, spraying and drying to obtain algae powder health-care food. It creates 'animals-fowls-marsh-fish-algae-bacterium' symbiotic food-chain circulation and ecological balance system.