Abstract: The simultaneous relationship between the North Atlantic Oscillations (NAO) and the precipitation over Southwest China in boreal winter is investigated using the NCEP/NCAR reanalysis data and 160 Chinese stations monthly rainfall datasets during 1951－2010. The results show that there is a significant positive correlation between the boreal winter NAO index (INAO) and the winter precipitation in Southwest China. Moreover, the positive correlation is asymmetric. During the winter of weak NAO years, the circulation pattern in East Asia is not favorable for precipitation in Southwest China. Contrastingly, during the winter of strong NAO years, the relationship between them is not significant. Further analysis shows that the main circulation pattern which influences the precipitation in Southwest China is a teleconnection pattern existed in the Caspian Sea and Middle East-Arabian Sea-Tibetan Plateau and the downstream area (CAT teleconnection). It is found that the CAT teleconnection pattern has an asymmetric relationship with the winter NAO, and the relationship is significant only in the winter when the NAO is in its negative phase. The results from the composite of the wave ray and the wave activity flux during strong and weak winter NAO years show that in weak winter NAO years the wave rays which were aroused by the wave sources in the Mediterranean could be consistent with the route of the CAT teleconnection pattern, and the wave-activity flux shows that the stationary wave could spread to the downstream along the Caspian Sea and Middle East Arabian Sea-Tibetan Plateau. On the other hand, in strong winter NAO years, the wave rays are to the north of the CAT teleconnection and the stationary wave could spread only to Indian Peninsular. These results indicate that the asymmetric relationship between the winter NAO and the winter rainfall over Southwest China is determined by the asymmetric influence of NAO on the CAT teleconnection.