NOVELTY - Methanogenic composite microbial inoculum includes Methanosarcina acetivorans DSM-No.2834 and Methanobacterium formicicum DSM-No.1535. Methanobrevibacter arboriphilicus DSM-No.1125, Methanolobus tindarius DSM-No.2278 and Methanosaetaconcilii DSM-No.6752 are also provided, which are preserved in German culture preservation centre as inoculation methane bacteria. The inoculum is inoculated in liquid methane bacteria culture medium under anaerobic conditions, and are enlarged and cultured in singles.    USE - Methanogenic composite microbial inoculum for use in marsh gas production.    ADVANTAGE - The methanogenic composite microbial inoculum ensures its intermediate propagation at the starting time of marsh gas production, and improves gas-producing efficiency and stability of methane tank.    DETAILED DESCRIPTION - Methanogenic composite microbial inoculum includes Methanosarcina acetivorans DSM-No.2834 and Methanobacterium formicicum DSM-No.1535. Methanobrevibacter arboriphilicus DSM-No.1125, Methanolobus tindarius DSM-No.2278 and Methanosaetaconcilii DSM-No.6752 are also provided, which are preserved in German culture preservation centre as inoculation methane bacteria. The inoculum is inoculated in liquid methane bacteria culture medium under anaerobic conditions, and are enlarged and cultured in singles. The bacterium fluids of the methane bacteria are mixed after being cultured in to obtain liquid methanogenic composite microbial inoculum. An INDEPENDENT CLAIM is included for a method for preparing methanogenic composite microbial inoculum, which involves:    (A) taking all mentioned bacterial strain as inoculation methane bacteria;    (B) inculating the bacteria in liquid methane bacteria culture medium;    (C) culturing the bacteria in each stage for 5-8 days at 35 degrees C under anaerobic conditions;    (D) obtaining bacterium fluids of the methane bacteria; and    (E) mixing the bacterium fluids of the methane bacteria to obtain liquid methanogenic composite microbial inoculum.    .