NOVELTY - Urban human excrement dry fermentation marsh gas is prepared by sterilizing excrement collected in tank, preparing dehydrated cake material, air-drying the cake and rolling the cake into ball, selecting sludge at the bottom of waterlogged compost tanks or old marsh gas residues of the marsh gas tank as inoculum, mixing the dry fecal particles and plant straw, passing 1/2 of the mixed material into the tank, inoculating the inoculum into the remaining material, adding the mixture into the tank, and adding water to the dried material, and sealing the tank.    USE - As urban human excrement dry fermentation marsh gas.    ADVANTAGE - The marsh gas is environmentally-friendly and prepared by fully utilizing the excrement and the plant straws and hence resources are rationally utilized. The marsh gas residue can be reused by agriculture in the suburbs and hence virtuous cycle during environmental management is realized.    DETAILED DESCRIPTION - Urban human excrement dry fermentation marsh gas is prepared by (a) collecting septic tank sewage of each resident living area in excrement storage tank, sterilizing and deodorizing the excrement in the tank by adding sodium hydroxide solution and lime milk to the tank, and controlling the pH of 6-8, floating, diluting, and depositing the excrement, depriving clear liquid portion, pressing surplus slurry, filtering the slurry and preparing dehydrated cake material, air-drying the cake, rolling the cake into ball using ball rolling machine, and drying and packaging the cake for further use, (b) selecting sludge at the bottom of waterlogged compost tanks in which bubbles are frequently generated or old marsh gas residues of the marsh gas tank as inoculum, (c) mixing the dried fecal particles and plant straw, passing 1/2 of the mixed material into the marsh gas tank, inoculating the inoculum into the remaining mixed material, adding the mixture into the marsh gas reaction tank, and adding water to the dried material, where the mass of the dried material is 15-25%, and (d) maintaining the reaction temperature at 40-50 degrees C, sealing the marsh gas reaction tank till the internal pressure of the tank reaches 3-4 KPa, and deflating the marsh gas till the pressure reaches 2 KPa.