The invention relates to an installation device of a submersible mixer for an anaerobic reactor. The device comprises a tank wall, a manhole, guide rods, a connecting bracket, safety covers and the like, wherein a plurality of guide rods are installed at a position close to the tank wall inside the anaerobic reactor according to the amount of the submersible mixer, lower limiting positions of the submersible mixer are welded at certain heights on the guide rods, the safety covers for preventing methane from escaping out are arranged on the upper portions of the guide rods, fixed pulleys for lifting the submersible mixers are installed below the safety covers on the guide rods, a manual capstan for lifting the submersible mixers is arranged on the inspection manhole, and a cable discharging device provided with water seal is adopted for leading cables out of the anaerobic reactor so as to prevent the methane from escaping. According to the installation method, a submersible pump can be installed inside the anaerobic reactor conveniently, and the problem that the submersible mixer cannot be applied to the anaerobic reactor is solved.