NOVELTY - Producing marsh gas by dry anaerobic fermentation using sewage sludge, involves piling up dewatered sludge in aerobic condition for 2-3 days for reducing velocity and water ratio of the sludge, adding the pre-treated sludge into acid-production fermentation pot, adding aerobic granular sludge, or biogas residues, subjecting the material to acid-production fermentation in aerobic or anaerobic conditions, and then methane-production fermentation in anaerobic condition, and recovering product.    USE - The method is useful for producing marsh gas and organic fertilizer.    ADVANTAGE - Equipment investment and land occupation rate are reduced compared to wet fermentation technology.    DETAILED DESCRIPTION - Method for producing marsh gas by dry anaerobic fermentation using sewage sludge, involves piling up dewatered sludge in aerobic condition for 2-3 days for reducing velocity and water ratio of the sludge, where the water ratio is reduced to 10-20% and the temperature of the material is increased; adding the pre-treated sludge into acid-production fermentation pot, adding aerobic granular sludge (20-30% of the volume of the inoculation material), or biogas residues, where the inoculation material is 20-30% of the volume of the fermentation material, mixing and maintaining the inoculation material statically for 6-8 days; subjecting the material to acid-production fermentation in aerobic or anaerobic conditions, maintaining the concentration of oxygen at 2% or less, stirring material using helix ribbon type or anchor ribbon type stirrer, controlling pH value of the material so that the intermediate product and energy in the acid production stage can be transferred and diffused in the material sufficiently, and controlling the time of the acid production stage at 15-20 days; adding the material after the acid production stage into a methane-production fermentation pot, performing methane-production fermentation in anaerobic condition, mixing the product using extrusion type stirring such that the fermentation material and the product are micro-mixed sufficiently and the gas in the material in the fermentation process overflows sufficiently, maintaining the temperature of the material at the methane production stage at 34-36 degrees C, adjusting the pH of the material at the methane production stage to 6.6-7.5; and recovering biogas residue, using one part of the biogas residue after the methane production stage as the inoculation material of the next batch of fermentation sludge, and performing aerobic composting stabilization to the remaining material so that the stabilized material can enter the sludge composting process for performing organic fertilizer processing treatment.