NOVELTY - Stirring control method for biogas digester comprises using a rotation resistance test instrument to detect a resistance value which can characterize the quantity of floating materials on the surface of marsh gas slurry in the marsh gas tank; comparing the resistance value with a preset resistance threshold, and judging whether the resistance value is bigger than the preset resistance threshold; and when the resistance value is bigger than the preset resistance threshold, generating a stirring signal, and sending to a stirrer.    USE - The stirring control method or system is useful for biogas digester (claimed).    ADVANTAGE - According to the method, the resistance on the surface of the marsh gas slurry can be detected, so that when the quantity of the floating materials on the surface of the marsh gas slurry is enough to influence the gas production condition of the marsh gas tank, the stirrer is controlled to perform stirring, thus preventing the floating materials from influencing the gas production condition.    DETAILED DESCRIPTION - Stirring control method for biogas digester, where the biogas digester is provided with a stirrer in the marsh gas tank, the stirrer vertically passes through the inner space, and the marsh gas tank is provided with a floating rotary resistance tester of the biogas liquid surface of the methane tank of the marsh gas tank, comprises using a rotation resistance test instrument to detect a resistance value which can characterize the quantity of floating materials on the surface of marsh gas slurry in the marsh gas tank; comparing the resistance value with a preset resistance threshold, and judging whether the resistance value is bigger than the preset resistance threshold; and when the resistance value is bigger than the preset resistance threshold, generating a stirring signal, and sending to a stirrer. An INDEPENDENT CLAIM is a stirring system for biogas digester, comprising a stirrer, a floating platform, a rotating resistance tester and a controller, where the stirrer is vertically set in the marsh gas tank, and the stirrer vertically penetrated in the marsh gas tank space, the floating platform includes: a slide rail on the marsh gas tank wall and capable of sliding along the slide rail, and can float on the supporting platform of the marsh liquid surface of the marsh gas tank, the rotating resistance tester is mounted on the supporting platform, which is used for detecting the characteristic resistance value floating number of the biogas liquid surface of the marsh gas tank, the first controller is connected with the stirrer, rotating resistance tester is connected with the resistance value for the rotational resistance tester with preset resistance threshold value and greater than the preset resistance threshold value when the resistance value to generate the mixing signal and output to the mixer.