The composition, seasonal variation and sources attribution of volatile organic compounds (VOCs) were investigated in a plateau city in China. Air samples were collected simultaneously by canister at three sites and covered four seasons. 113 VOCs species were determined by GC–MS–FID. Higher concentration of α-pinene (0.98 ± 2.25 ppb) in urban central site was observed in this study than in most others reported. Results of the ratios of α-pinene/isoprene, source profile of VOCs and backward trajectory of air mass identified that both biogenic emission and wooden furniture manufacturers were contributors to the significant high concentration of α-pinene. And high concentration of α-pinene (>2 ppb) accompanied by significant high concentration of isopentane, for air mass passing through the dense area of both wooden furniture factories and gas stations. In addition, the highest concentrations of alkanes, anthropogenic alkenes, alkynes, aromatics and halohydrocarbons appeared in winter, caused by the lowest temperature and mixed layer height in winter. For biogenic alkenes, the highest concentration was found in spring or summer as plants flourishing. Finally, results of the ratios of species and PMF model showed that local vehicle, fuel evaporation and household were the dominant VOCs source with contribution to 42.7%–53.5% of the total VOCs concentration.