In China, due to the high density of population and vehicles in megacities, the commercial center and high-rise residential buildings have been widely equipped with large underground parking garages (UPGs). Volatile organic compounds (VOCs) and particulate matters (PM) have been confirmed as major pollutants in underground parking garages. And therefore, exposure to these air pollutants, especially ultrafine particles and BTEX (benzene, toluene, ethylbenzene, and xylenes), is closely associated with the health of the car owners or the garage workers. This study sampled or online monitored the concentrations of benzene, toluene, xylenes, formaldehyde, TVOC (total volatile organic compounds), PM_2.5, and PM₁₀ in the underground garage of three commercial center and high-rise residential buildings. The time-weighted average (TWA) concentrations of pollutants in the underground garage in the commercial center/high-rise residential buildings were as follows: benzene 0.12/0.11 mg·m⁻³, toluene 0.33/0.31 mg·m⁻³, xylenes 0.23/0.20 mg·m⁻³, TVOC 1.04/1.19 mg·m⁻³, PM_2.5 0.20/0.19 mg·m⁻³, and PM₁₀ 0.24/0.22 mg·m⁻³. Indoor PM concentrations were slightly higher than outdoor PM concentrations, and there was a significant positive relationship between the difference of I/O PM concentrations and traffic volume. This paper also compared and analyzed BTEX concentration ratios (e.g., toluene/benzene and xylenes/benzene) at every sampling point of different underground garages. These ratios were compared and analyzed to evaluate the influence of vehicle emissions and outdoor air quality on the spatial distribution of indoor air quality quantitatively.