NOVELTY - A preparation device for preparing methane gas with organic waste comprises methane collector (14) for storing methane; methane reactor (11) for preparing methane gas; an acid processor (1) for acid processing the organic waste; an alkali processor (2) for alkali processing the organic waste; and an acid reactor (8). The acid processor is connected with alkali processor, which is connected with acid reactor. The acid reactor is connected with methane reactor, which is connected with methane collector.    USE - Preparation device for preparing methane gas with organic waste (claimed).    ADVANTAGE - The device can increase efficiency of methane yield by 50-120%. The method of preparing methane gas using the device is simple and effective, energy-saving, and of low-cost; and if potassium hydroxide is used, organic potash fertilizer can be obtained.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method of preparing methane gas using the preparation device comprising:    (A) adding 5-15 ml acid solution into every 1 g of organic waste to be processed in the acid processor (1) for 4-24 hours at normal pressure, where the concentration of acid solution is 0.1-0.6 N;    (B) adding 5-15 ml alkali solution into every 1 g of organic waste to be processed in the alkali processor (2) for 4-24 hours at normal pressure, where concentration of alkali solution is 0.1-0.6 N;    (C) neutralizing organic waste and acid solution in the acid processor with that in the alkali processor;    (D) packing the organic waste and acid solution in the alkali processor into acid reactor (8) filled with acid slurry, where organic waste and acid solution react with acid slurry to generate acidulated liquid;    (E) introducing intermittently the acidulated liquid into the methane rector filled with methane slurry at a frequency of 4-12 times every day, where volume of acidulated liquid is 10-60% to the total volume of liquid in the acid reactor in each time; and    (F) fermenting the acidulated liquid with the slurry in methane reactor (11) for 15-20 days to obtain methane gas.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view of a preparation device for preparing methane gas with organic waste.    Acid processor (1)    Alkali processor (2)    Acid reactor (8)    Methane reactor (11)    Methane collector (14)