To  investigate  the  effects  of  anaerobic  fermentation  with  different  inoculants  on  the pyrolysis behavior of biomass, this study used biogas residues from anaerobic digestion of corn straw inoculated  with  rumen  fluid  and  sludge  as  examples.  The  pyrolysis  characteristics  of  the  materials before and after anaerobic fermentation were analyzed using thermogravimetric analysis and pyrolysis-gas  chromatography-mass  spectrometry  (PY-GC-MS)， and  the  resulting  biochar  was  characterized. The results indicated that the apparent activation energy required for the pyrolysis of biogas residues was  higher  than  that  of  the  raw  material  before  fermentation， indicating  greater  thermal  stability. Furthermore，the activation energy required for the pyrolysis of sludge-fermented biogas residues was higher  than  that  for  rumen  fluid-fermented  biogas  residues.  The  volatile  products  generated  during pyrolysis were predominantly phenolic compounds and carbonyl compounds. The biochar yield from biogas residues was significantly higher than that of the raw material，exceeding 60% in both cases. Compared to the raw material，biochar from biogas residue showed increased surface roughness and porosity，resulting in higher specific surface area and porosity. Additionally，the biochar from sludge fermentation had a higher specific surface area and porosity than that from rumen fluid fermentation， though the relative content of pyrrolic-N was higher in the latter. This study provides a reference for the resource utilization of biogas residues.