Based on the data sets of Ozone Monitoring Instrument (OMI) O3 profiles over the Tibetan Plateau and the NCEP/NCAR reanalysis data in July 2006, the relationships between low O3 over the Tibetan Plateau and the longitudinal oscillation of the South Asia high are analyzed. The results show that the longitudinal oscillation of the South Asia high has an obvious correlation with the low O3 over the Tibetan Plateau. When the South Asia high exhibits the east (west) phase, the low O3 centers of the total column O3, the tropospheric column O3, and the stratospheric column O3 are located in the east (west) of the Tibetan Plateau. During the west phase of the South Asia high, the low O3 air is difficult to transport to the top of the Tibetan Plateau and the low O3 is weak over the Tibetan Plateau. While during the east phase of the South Asia high, the low O3 air from the Bay of Bengal is transported northward to the middle troposphere over the Tibetan Plateau by southeast currents and piles over the Tibetan Plateau， forming the low O3. So the longitudinal oscillation of the South Asia high is one of the most important factors contributing to the variation of the low O3 over the Tibetan Plateau, and the study is good for understanding the mechanism of the longitudinal oscillation of the South Asia high and improving the quality of climate forecast in China.