NOVELTY - Producing methane comprises killing methane-producing microorganisms in an auxiliary methane-producing pool (8) by germicidal UV lamp (12) at regular intervals and returning raffinate of the auxiliary methane-producing pool to a main methane-producing pool (6) to increase the pH of hydrogen-producing environment.    USE - Production of methane.    ADVANTAGE - The method resolves the problem of hydrogen production-inhibiting reduced pH caused by organic acid and microorganisms and achieves the circulating utilization of the raffinate of hydrogen production. The system has reduced amount of discharge, achieving non-chemical substances regulation and control of pH, avoiding environmental pollution and increasing economic benefit.    DETAILED DESCRIPTION - Producing methane comprises producing hydrogen in main hydrogen-producing pool (2) and in auxiliary hydrogen-producing pool (4). Raffinate of the auxiliary hydrogen-producing pool is introduced to a main methane-producing pool (6) and an auxiliary methane-producing pool (8) to produce methane from organic mater in the raffinate, e.g. organic acid and sterols and the unreacted raw material in hydrogen production. The organic acid is decomposed and the pH of the auxiliary methane-producing pool is controlled to 7.0-9.0. Methane-producing microorganisms in the auxiliary methane-producing pool are killed through germicidal UV lamp (12) at regular intervals and the raffinate of the auxiliary methane-producing pool is returned to the main methane-producing pool to increase the pH of the hydrogen-producing environment. An INDEPENDENT CLAIM is included for a methane production system comprising hydrogen-producing pool (1), methane-producing pool (5), baffle plates (3, 7), fresh feed pump (14), hydrogen output tube (16), pump (9-11, 13), methane output tube (17), germicidal UV lamp (12), and exhaust pump (15).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of a methane production system.    Hydrogen-producing pool (1)    Main hydrogen-producing pool (2)    Baffle plates (3, 7)    Auxiliary hydrogen-producing pool (4)    Methane-producing pool (5)    Main methane-producing pool (6)    Auxiliary methane-producing pool (8)    Pump (9-11, 13)    Germicidal UV lamp (12)    Fresh feed pump (14)    Exhaust pump (15)    Hydrogen output tube (16)    Methane output tube (17)