NOVELTY - Producing biogas by combined solid state fermentation of crop straws and excrements of livestocks, comprises: using three process including solid crop straw solid pre-treatment, solid-state fermentation and biogas combined pyrolysis.    USE - The method is useful for producing biogas by combined solid state fermentation of crop straws and excrements of livestocks (claimed).    ADVANTAGE - The pyrolysis gas generated can be used to supply heat to the system, and the solid product after pyrolysis can be used as an active adsorbing material or a catalytic material, so that comprehensive utilization of organic wastes is realized. Compared with the prior art, the method for producing biogas has the characteristics of no biogas slurry, convenience and rapidness, safety, stability and high biogas producing efficiency.    DETAILED DESCRIPTION - Producing biogas by combined solid state fermentation of crop straws and excrements of livestocks, comprises: using three process including solid crop straw solid pre-treatment, solid-state fermentation and biogas combined pyrolysis: (a) crops straw solid pretreatment: rubbing the crop straws by a rubber; adding sodium hydroxide (NaOH) aqueous liquor, and uniformly mixing for pretreatment, NaOH is added in an amount of 3-7 wt.%, mixed moisture content of crop straw is 50-60 wt.%, the mixed crop straw is in 20-30 degrees C for 3 days under the conditions, no liquid out of the whole process; (2) fermentation: performing combined solid fermentation on mixed crop straws, excrements of livestocks with a ratio of (1:1)-(3:1) and inoculums (3:1)-(4:1); performing anaerobic fermentation to produce biogas at 50-60 degrees C, in the entire process without adding extra nutrients and regulating pH value; (3) biogas residue pyrolysis: taking out residue after solid fermentation, 20-40% of the residue is used for newly added inoculums and the rest enters into a pyrolysis reactor for pyrolysis to produce biogas, starting from room temperature to 30-50 degrees C/minute heating rate to reach the final temperature of 600-800 degrees C for 1.5-3 hours.