Abstract: Using the NCEP/NCAR FNL data and the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim data and the Ozone Monitoring Instrument (OMI) ozone profile data,together with a regional atmospheric chemical model (WRF-Chem), a tropopause folding event caused by a cold trough during 19-21 March 2012 was analyzed.The contributions of advection, turbulence mixing and convective transport processes to the transport of the stratospheric ozone to the troposphere are diagnosed.The results show that the tropopause folding event occurred in the northwest side of the Tibetan Plateau is located in the transition zone between the tropical tropopause and the mid-latitude tropopause.Due to steep north-south gradient of the tropopause, the stratosphere and troposphere exchange (STE) in this region is more persistent and stronger than that caused by the east-west tropopause folding.Mass exchange across the isentropic surface and the turbulent mixing have significant contributions to the STE.The higher orography has a significant influence on the STE processes with its effect having an evident diurnal variation.In the morning and evening time, the upward motions due to forcing lift of the high orography are strong and inhibit the mass exchange between stratosphere and troposphere.In the afternoon, the thermal effect of the high orography enhances, and the turbulent mixing near the top of the mountain leads to significant ozone increases in the upper troposphere with the development of local circulation on the leeward slope of the high orography,and, the higher the orography is the more significant this effect is.The height of the orography of 2.5 km is critical in term of the turbulent mixing. Above this height, the contribution of turbulent mixing to ozone change increases about 1% when the average height of the orography rises 100 m.