Homogeneous cellulose and hetergenous oak leaves with montmorillonite as a catalyst were used as a biomass to investigate bio-gas and bio-oil. The results show that the loading of montmorillonite promotes the conversion of cellulose pyrolysis to β-elimination pathways, leading to an increase in activation energy and DTG peak temperature, but has little effect on the pyrolysis characteristics of oak leaves. Montmorillonite can catalyze the secondary cracking of biomass pyrolysis liquid products, which reduces the liquid yield and increases the gas yield, but has little effect on the solid product yield. Pyrolysis gases are mainly H₂, CH₄ and CO₂. The surface and layers of montmorillonite contain the Lewis and Brønsted acid sites, which can catalyze the decarboxylation reaction of carboxylic acids in situ and degrade their yield, and has a promoting effect on the furfural and levoglucosenone enrichment of bio-oil.