Abstract: The catalytic behaviors of Ca-modified HZSM-5 during oil shale pyrolysis process were investigated in a tubular rector and by TG-MS-FTIR. The physicochemical properties of the molecular sieve were characterized by BET, NH₃-TPD, and TG. The results show that the molecular sieve can significantly increase yields of C₁₋₄ aliphatic hydrocarbons and reduce their evolution temperatures. After modified, Ca/HZSM-5 can reduce yields of CO₂, increase yields of shale oil and decrease lengths of aliphatic chains in shale oil. But Ca/HZSM-5 has a strong catalytic effect on aromatization. Brönsted acid sites have an obvious catalytic effect on aliphatic hydrocarbons, while Lewis acid sites are more targeted at aromatization process of pyrolysis products.