NOVELTY - A Clostridium butyricum SZ11 (CGMCC No. 4703), is new.    USE - The C. butyricum SZ11 is useful for pretreating fermenting materials to increase the fermenting gas yield of low temperature methane (claimed).    ADVANTAGE - The method above can perform the regular methane fermentation at 15-20 degrees C so as to reduce the temperature change effect of gas in the methane-generating pit and increase the gas yield of methane-generating pit by 10%. The fungicide will not cause secondary environmental pollution; and the fermented biogas residue and biogas slurry added with fungicide can produce excellent fertilizer.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is a method for pretreating fermenting materials by using the C. butyricum SZ11 (CGMCC No. 4703) so as to increase the fermenting gas yield of low temperature methane, by (a) preparing water and pre-fermenting materials into a pretreatment mixture, where the water content if 60-80%; (b) activating C. butyricum SZ11: preparing an activated culture medium comprising 10 g/L tryptone, 5 g/L beef extract, 3 g/L yeast extracts, 10 g/L glucose, 50 g/L composite salt and 0.25 g/L cysteine hydrochloride; the activated culture medium is sterilized at 115 degrees C for 15 minutes so as to prepare activated culture liquid of C. butyricum SZ11; the composition of composite salt is 1 g/L dipotassium hydrogen phosphate (K2HPO4), 0.5 g/L potassium dihydrogen phosphate (KH2PO4), 0.2 g/L calcium hypochlorite (CaCl2O), 0.4 g/L magnesium sulfate heptahydrate (MgSO4.7H2O), 0.05 g/L ferrous sulfate heptahydrate (FeSO4.7H2O) and 0.5 g/L manganese sulfate monohydrate (MnSO4.H2O); pinking the single bacterial colony from an anaerobic rolling pipe and inoculating into the anaerobic pipe comprising 10 mL activated culture medium, cultivating below 37 degrees C for 45-55 hours so as to obtain the activated bacterial colony; (c) cultivating C. butyricum SZ11 seed; preparing seed culture medium comprising 5.0 parts by weight of tryptone, 5.0 parts by weight of beef extract, 10 parts by weight of yeast extracts, 5.0 parts by weight of glucose, 0.5 parts by weight of cysteine hydrochloride, 40 parts by weight of saline solution and 1000 parts by weight of distilled water; using inorganic acid or inorganic alkali to adjust pH until the pH value is 7.2-7.5, and sterilizing at 115 degrees C for 12-18 minutes so as to obtain the culture medium of C. butyricum SZ11 seed; the saline solution is prepared by dissolving 0.25 parts by weight of calcium chloride dihydrate (CaCl2O.2H2O), 0.5 parts by weight of MgSO4.7H2O, 1 part of K2HPO4, 1 part of KH2PO4, 10 parts by weight of sodium bicarbonate (NaHCO3) and 2 parts by weight of sodium chloride (NaCl) by using 1000 parts by weight of distilled water; seed cultivation: the culture medium is added with 5% activated bacteria obtained in step (b), and cultivating below 37 degrees C for 10-14 hours so as to prepare the seed liquid; (d) fermentation culture of C. butyricum SZ11: mixing 40.0 parts by weight of bean cake powder, 4.0 parts by weight of corn pulp, 20.0 parts by weight of glucose, 0.75 parts by weight of cysteine hydrochloride, 40 parts by weight of saline solution and 1000 parts by weight of distilled water, using the inorganic acid or inorganic alkali to adjust pH until the pH value is 7.2-7.5, and sterilizing at 115 degrees C for 12-18 minutes; preparing saline solution by dissolving 0.25 parts by weight of CaCl2O.2H2O, 0.5 parts by weight of MgSO4.7H2O, 1 part of K2HPO4, 1 part of KH2PO4, 10 parts by weight of NaHCO3 and 2 parts by weight of NaCl by using 1000 parts by weight of distilled water; fermentation cultivation: the culture medium is added with 5% seed liquid of C. butyricum SZ11 obtained in step (c), and cultivating at 37 degrees C for 45-55 hours with a stirring rate of 100 rounds per minute (rpm) so as to obtain fermented liquid containing 2.0-3.0 x 107 C. butyricum SZ11; (e) the pretreatment mixture obtained in step (a) is added with 4-8% C. butyricum SZ11 fermenting liquid in step (d), and then pre-fermented at 21-30 degrees C for 20-30 hours so as to obtain a pre-fermented product; and (f) the pre-fermented product in step (e) is added to the methane fermenting pit, then added with biogas residue or biogas slurry which is 1-1.5 times of the pre-fermented product, and then added with appropriate amount of water for being mixed so that the water content of the mixture is 90-96% and performing the regular methane fermentation at 15-20 degrees C.