Abstract: Anaerobic co-digestion technology for kitchen waste and waste activated sludge has been widely applied. Digestate containing fulvic acids (FA) and humic acids (HA) can accelerate interspecies electron co-transfer and can be recycled as a potential carbon source. An anaerobic co-digestion system was established using kitchen waste and waste activated sludge pretreated by thermal hydrolysis. The effects of the addition of biochar (BioC)/zero-valent iron (ZVI), digestion temperature, and thermal hydrolysis time on proteinaceous substances, FA, and HA were investigated. Appropriately extending the thermal hydrolysis pretreatment time effectively increased the COD of co-digestion of kitchen waste and sludge, accelerated the conversion of total nitrogen to ammonia nitrogen, and increased humic-like substances to promote anaerobic digestion. The addition of ZVI or BioC effectively increased biogas production and promoted the conversion of FA and HA. Experiments revealed that with a thermal hydrolysis time of 30 min and a BioC dosage of 5 g/L, the maximum daily biogas production reached 2036.1 mL, FA reached a maximum of 3 306.8×10⁶ a.u.nm², and HA reached up to 2 707.3×10⁶ a.u.nm². With a thermal hydrolysis time of 60 min and a ZVI dosage of 2 g/L, the maximum daily biogas production reached 558.70 mL, FA reached a maximum of 4 912.96×10⁶ a.u.nm², and HA reached up to 3 482.11×10⁶ a.u.nm². Optimization by response surface methodology indicated that the model was significant in the BioC group, with the rank of factor importance being: BioC dosage > thermal hydrolysis time > digestion temperature. The optimal experimental conditions were a BioC dosage of 15.0 g/L, a thermal hydrolysis time of 30 min, and a digestion temperature of 25 ℃. Under these conditions, the contents of protein-like substances, FA, and HA in the anaerobic co-digestion system were 1 557.75×10⁶, 1 063.07×10⁶, and 1 528.23×10⁶ a.u.nm², respectively. This research provides key parameters for the co-digestion of kitchen waste and waste activated sludge and the resource utilization of biogas slurry, and optimizes the operational parameters for their synergistic anaerobic digestion.