The geological conditions of the western Sichuan Plateau are complex, and the problem of harmful gases in the process of tunnel construction has become increasingly prominent, which has brought unprecedented geological challenges to the western development strategy. In view of the complex distribution of harmful gases in western Sichuan, based on the collection and analysis of regional geological data and tunnel data in the western Sichuan plateau, the study is conducted using geological history analysis, oil and gas accumulation theory, field detection and other methods main components of harmful gases in the complex structural area of western Sichuan. The results show that: The are gas (methane), hydrogen sulfide and carbon dioxide. There are two kinds of harmful causes: inorganic causes and organic causes. Gas mainly comes from organic causes, hydrogen sulfide mainly comes from inorganic causes, and carbon dioxide is mixed causes. Harmful gases are mainly distributed in the core area of folds, deep strata, near compression-torsion faults, carbonaceous strata or igneous rocks or metamorphic rocks, and the distribution rules are interrelated. The research results have a guiding affect on the prediction and control of harmful gases in the tunnels of western Sichuan Plateau.