Abstract: Chain hydrocarbons cracking always occurs in pyrolysis/gasification. Among them, the reaction time of light chain hydrocarbons is short and they have many reaction paths, which make it difficult to accurately detect and analyze each evolution path by experiment. In this study, Gaussian and its related software were employed to predict the reaction sites and to study the chain cracking mechanism of C₂ chain hydrocarbons (including ethane, ethylene and acetylene) under the action of H/OH/O radicals or H₂O. According to the results, radicals can both attack the C and H atoms of ethane, while the C atoms of ethylene and acetylene are the main attack sites. Among the above radicals, OH radical is the best for unsaturated hydrocarbons cracking, while H radical is the best for saturated hydrocarbons, showing that the steam is conducive to the cracking of C₂ chain hydrocarbons in actual process. In addition, comparing the optimal path of the reaction of ethylene or acetylene with OH radical, it can be found that CH₂CH₂OH radicals are easier to crack than CH₂CHO radicals below 1200 K, while CH₂CHO radicals are easier to crack above 1200 K, inferring the better response speed of aldehyde groups for temperature than alcohol groups.