During the peak tourist season, the CO2 concentration in some caves in Mogao Grottoes often exceeds 1500 ppm. A mechanical ventilation system for Cave 328 of Mogao Grottoes is thereby designed and the experiment is conducted in January and February of 2015. The results indicate that the air exchange rate has improved from 3.2 h(-1) in the case of natural ventilation to 6 h(-1) in mechanical ventilation, while the air turbulence merely increases from 0 to 0.05 m/s in the body of the cave and 0.15-0.2 m/s in the aisle in natural ventilation to 0-0.1 m/s in the body of the cave and 0.2-0.3 m/s in the aisle in mechanical ventilation. It is thus concluded that the mechanical ventilation system effectively increases the air exchange rate without causing noticeable disturbance of the air in the cave, and the protective environment of the cave is sustained. A theoretical reference can be hopefully provided in the design and implementation of the mechanical ventilation system in Mogao Grottoes. (C) 2016 Elsevier B.V. All rights reserved.