Straw waste has a large amount of lignocellulose, which shows a strong resistance to biodegradation in the composting process and hinders the formation of humic substances. Therefore, the effects of pH adjustment and inoculation of degradation bacteria on the composting process, lignocellulose degradation and humus formation in secondary fermentation were explored through aerobic composting experiments. The experiment was designed with four treatment groups: CK (conventional composting), T1 (adjusting pH), T2 (inoculating P. chrysosporium), and T3 (adjusting pH and inoculating P. chrysosporium), respectively. Results showed that except for treatment CK, all other treatments met the maturation standards at the end of composting. Adjustment of the pH value and the inoculation of Phanerochaete chrysosporium (P. chrysosporium) can significantly shorten the fermentation time. Among them, the lignin content of treatment T3 was reduced significantly by 14.28% compared to treatment T2; the content of humic acid in T3 increased significantly by 51.32% and 14.04% compared with T1 (adjusting pH) and T2 (p < 0.05), respectively. In terms of key enzyme activity and precursor substance changes, the pH adjustment treatment was superior to other treatments after composting. This study confirmed that the change of pH conditions is an important environmental factor for microorganisms to enhance the humification process; degrading enzymes were used as a “bridge” to enhance the continuous degradation of lignocellulose by microorganisms and increase the supplementation of precursors and the synthesis of humic acid, which is the mechanism to enhance the humification process. Our findings provided a new method to enhance the humification process, which is a valuable and economical technical approach to improve organic fertilizer quality.