The excessive oxygen content in biomass obstructs the production of high-quality bio-oils. In this work, we developed a tandem catalytic bed (TCB) of CeO2 and HZSM-5 in an analytical pyrolyzer to enhance the hydrocarbon production from co-pyrolysis of corn stover (CS) and LDPE. Results indicated that CeO2 could remove oxygen from acids, aldehydes and methoxy phenols, producing a maximum yield of hydrocarbons of 85% and highest selectivity of monocyclic aromatics of 73% in the TCB. The addition of LDPE exhibited a near-complete elimination of oxygenates, leaving hydrocarbons as the overwhelming products. With increasing LDPE proportion, the yield of aliphatics and the selectivity of BTX kept increasing. An optimum H/C-eff of 0.7 was superior to that reported in literature. Mechanisms consisting of deoxygenation, Diels-Alder reactions, hydrocarbon pool and hydrogen transfer reactions were discussed extensively. Our findings provide an efficient method to produce high-quality biofuels from renewable biomass resources.