Using multiple dataset and based on statistical analysis method, this paper has investigated the relationship between La Nina and the winter temperature in Southwest China (Sichuan, Chongqing, Guizhou, and Yunnan provinces) during 1970-2019. The results reveal that the influence of La Nina on the winter temperature in Southwest China shows an interdecadal variation feature. During 1970-1996, La Nina events lead to a cold and dry winter in Southwest China. During 1997-2019, however, La Nina events may cause a cold and wet winter or a warm and dry winter in Southwest China. Further analysis shows that the 500-hPa geopotential height over Qinghai-Tibet Plateau (Tibet-H500 for short) played an important role as a bridge between La Nina events and the winter temperature in Southwest China. There is a close relationship between Tibet-H500 and La Nina, with the former lagging the latter for about five months. And their positive correlation also shows an interdecadal variation. During 1970-1996, Tibet-H500 is significantly positively correlated with the sea surface temperature anomaly (SSTA) in the equatorial central Pacific. La Nina events will weaken the Tibet-H500. Accompanied by the intensified Mongolian cyclone and the northwest-path cold air, they together lead to below-normal temperature in Southwest China. During 1997-2019, however, the Tibet-H500 is independent of the SSTA in the tropical ocean. Only strong La Nina events can decrease the Tibet-H500 and cause below-normal winter temperature in Southwest China, whereas during the winter of weak La Nina years, positive anomaly of Tibet-H500 still results in warm winter in Southwest China.
