Abstract: In this study, the characteristics and mechanisms of the stratosphere–troposphere exchange (STE) in deep convection over the southeastern part of the Qinghai–Xizang Plateau on August 12, 2010, were analyzed using the WRF-Chem model. It was revealed that the convection has the characteristics of penetrating convection, and the strong updraft in the convection can directly transport the air with high CO concentration and low O₃ concentration near the ground into the lower stratosphere. Thus, in the lower stratosphere, the concentrations of CO and O₃ increased and decreased, respectively. The deep convection also induced a strong turbulent mixing process, causing the continuous STE in the upper troposphere–lower stratosphere region within 3–4 h after the end of deep convection, transporting ice crystals, CO, and O₃ from the troposphere to the lower stratosphere. The water vapor that entered the lower stratosphere via the turbulent mixing process was reduced due to condensation and dehydration.