Abstract: Study on δ18O in precipitation at Nyalam in the south slope of the Himalayas shows that the δ18O in winter precipitation in the south of the Himalayasis quite different from that in the north of the Tibet an Plateau.δ18O in summer is characterized by low value.In winter,δ18O in precipitation is generally high.However,strong snow storm is characterized by extremely low value of δ18O in precipitation,which is in the same level as in the summer period.This phenomenon has an obvious effect on the ice core record in the south of the Tibet an Plateau,for the frequent snow storm in the south of Himalayas.On the one hand,the complexity of seasonal variation of δ18O in precipitation in the south to the Himalayas results in the difficulty of ice core dating in this area.On the other hand,δ18O in the ice core record in the south of the Tibetan Plateau includes not only the signal of summer monsoon,but also the winter storm.