NOVELTY - Promoting residual sludge methanogenesis using rust, comprises: adding high-solid sludge with rust into a sludge regulation pool, starting up fermentation tank, starting up electric stirrer for mixing; opening conveying pump for passing sludge into the inlet of anaerobic fermentation tank through a pipeline, closing the tank and carrying out anaerobic fermentation; and stopping aeration after the fermentation is finished, allowing it to stand for more than 6 hours for separation of sludge-water, discharging supernatant via discharge port and recovering rust using magnetic separator.    USE - The method is useful for promoting residual sludge methanogenesis using rust (claimed).    ADVANTAGE - The method is simple and economical, has strong processing capability and suitable for anaerobic fermentation device or upgrading the existing device.    DETAILED DESCRIPTION - Promoting residual sludge methanogenesis using rust, comprises: (i) adding high-solid sludge with rust and anaerobic microorganism into a sludge regulation pool, where the high-solid content in the sludge is less than or equal to 10%, and the surface area of the rust is less than or equal to 20 cm2, and mixing 1-20 g, preferably 10 g rust with 1 kg high-solid sludge, adding anaerobic microorganism derived from sludge into anaerobic fermentation tank discharge, mixing inoculation sludge with the high-solid sludge in a ratio of 1:9, starting up fermentation tank using anaerobic fermentation tank sewage treatment plant residual sludge as a seed sludge, starting up electric stirrer for mixing high-solid sludge with rust and anaerobic microorganism; (ii) opening the conveying pump for passing the sludge into the inlet of anaerobic fermentation tank through a pipeline, closing the tank and carrying out anaerobic fermentation for 20-25 days, preferably 22 days at 35-40 degrees C, preferably 37 degrees C, providing a nitrogen aeration device with the fermentation tank uniformly distributed with the air holes, where each air hole is spaced at distance of less than 50 cm with aerated flow of 10 l/minute, during anaerobic fermentation, the nitrogen aeration device starts every 2 hours with aeration of 30 minutes every time, where the sludge and rust completely mix in the tank, providing an air outlet on upper part of the fermenting tank for collecting generated methane; and (iii) stopping aeration after the fermentation is finished, allowing it to stand for more than 6 hours for complete separation of sludge-water, discharging the supernatant fluid via discharge port leaving behind 10% sludge as a seed sludge for the next fermentation, and remaining 90% as a residue, recovering rust of biogas using magnetic separator and re-using the rust for the next batch of fermentation.