A crude oil sample from the early mature stage of the Qingshankou Formation in the northern part of the Songliao Basin was mixed with different clay minerals (kaolin, montmorillonite, chlorite, and illite) in a certain proportion and placed in a quartz tube for sealing. The thermal simulation experiment was conducted using a high-pressure vessel closed continuous heating method. The results of hydrocarbon cracking gas show that as the temperature increases, the total production of cracked gaseous hydrocarbons (C1–C5) continues to increase, and 450 ℃ enters the peak of cracking. From the hydrocarbon composition in the cracking gas, pure crude oil is mainly composed of C1–C3, while C4–C5 in the cracking gas of crude oil + clay minerals also has a certain amount of distribution, with montmorillonite + crude oil being the most diverse and the highest content; The methane production of pure crude oil shows a V-shaped change with a turning point of 500 ℃, and the methane production of crude oil and clay ore shows a stepwise increase; The content of C2–C5 alkanes and olefins first increases and then decreases. The content of C2–C5 in the gaseous hydrocarbons generated by the cracking gas of crude oil and clay minerals is significantly higher than that of pure crude oil before 500 ℃; The carbon isotope of crude oil cracking gas is relatively light in the mature stage, and continuously heavier in the high over mature stage; At low temperatures, the isotopic composition of the cracking gas with added minerals is lighter than that of pure crude oil cracking gas. The carbon isotope difference between methane and ethane, as well as between ethane and propane, shows a gradually increasing trend. Moreover, when crude oil is cracked with the addition of minerals, except for montmorillonite, other clay minerals have an inhibitory effect on crude oil cracking at low temperatures (below 450 ℃). The inhibitory effect weakens with increasing temperature, and the cracking time of crude oil + montmorillonite is significantly earlier than that of pure crude oil, indicating that the participation of montmorillonite promotes crude oil cracking at low temperatures.