NOVELTY - Treating paper-making waste water using methane-producing anaerobic flora comprises adding sodium formate into straw pulp papermaking waste water in an anaerobic incubator, taking as methane enrichment culture medium, culturing, calculating total gas generated, detecting methane purity, transferring the culture medium into anaerobic bottle, expansion culturing by mixing paper making waste water and methane-producing anaerobic flora-anaerobic sludge mixture, reacting in upflow anaerobic sludge blanket (UASB), diluting, sampling every day to determine pH and chemical oxygen demand (COD).    USE - The method is useful for treating paper-making waste water using methane-producing anaerobic flora (claimed).    ADVANTAGE - The method: reduces the pH of the waste water, thus enabling the microflora to utilize organic substances in the waste water to generate marsh gas; has easy subsequent processing steps; is economical; improves the recovery rate; reduces secondary pollution; and provides socioeconomic benefit.    DETAILED DESCRIPTION - Treating paper-making waste water using methane-producing anaerobic flora comprises (a) taking 5 plus minus 1 g straw pulp papermaking waste water in an anaerobic incubator, adding 45 plus minus 5 ml sodium formate, taking methane enrichment culture medium into 100 ml anaerobic culture bottle using sodium acetate as substrate, maintaining hydrogen/carbon dioxide as substrate, allowing to stand and culturing for 10 plus minus 1 days at 30-35 degrees C, inoculating 5% inoculum into enrichment culture bottle containing methane enriched culture medium in the anaerobic incubator, allowing to stand, culturing for 10 plus minus 1 days at 30-35 degrees C, repeating 2-4 times, respectively taking sodium formate as a substrate for methane anaerobic flora, calculating gas generated in process, calculating for each 10 plus minus 1 days total gas content, simultaneously, respectively extracting 5 plus minus 1 ml gas, detecting methane purity in each gas by gas phase chromatography, where the methane enriched culture medium of pH 7.5 comprises 1 l distilled water, 1.25 g yeast powder, 0.5 g peptone, 0.5 g soybean peptone, 0.5 g L-cysteine hydrochloride, 0.544 g potassium dihydrogen phosphate, 1.3064 g disodium hydrogen phosphate and 1 ml resazurin, the prepared culture medium is transferred into the anaerobic bottle by filling nitrogen gas by air exchange process with a final concentration of 20 mM of sodium formate, or adding 20 mM sodium acetate, where the filling gas includes hydrogen, carbon dioxide and nitrogen in a ratio of 4:1:5, mixing the gases to obtain hydrogen/carbon dioxide as substrate for, sterilizing at 115 degrees C for 30 minutes, (b) inoculating 5% inoculum into methane enrichment culture medium when the methane purity reaches more than 70%, carrying out expansion culture until the optical density (OD) is 3-4, (c) mixing methane-producing anaerobic flora and anaerobic sludge in a volume ratio of 1:2, (d) taking alkaline straw or wood pulp paper making black liquor as paper making waste water sample, mixing 1 l paper making waste water, 3-4 l methane-producing anaerobic flora-anaerobic sludge mixture, and 5-6 l water, transferring into upflow anaerobic sludge blanket (UASB), reacting at 35-38 degrees C for 72 hours, diluting with 500-1000 ml water (10 times), sampling every day to determine pH, chemical oxygen demand (COD) index until the pH is 8-9 and COD is 50-60%, diluting with 500-1000 ml water (5 times), the COD removal rate when the pH is 8-9 is more than 50-60%, diluting with 500-1000 ml water (3.3 times), where the COD removal rate is more than 50-60% when the pH is 8-9, diluting with 500-1000 ml water (2.5 times), where the COD removal rate is more than 50-60% when the pH is 8-9, diluting with 500-1000 ml water (2 times), where the COD removal rate is 50-60% and the pH is 8-9, diluting with 500-1000 ml water (1.6 times), where the COD removal rate is 50-60% and the pH is 8-9, diluting with 500-1000 ml water (1.4 times), where the COD removal rate is 50-60% and the pH is 8-9 respectively each day, diluting with 500-1000 ml water (1.25 times), where the COD removal rate is 50-60% and the pH is 8-9 for 5-18 months, and processing paper-making wastewater. The straw pulp papermaking waste water has a pH of 11-12, COD of 11000-120000 mg/l. The wood pulp paper making waste water has a pH of 11-13 and COD of 106000-157000.