Considering the immigration from the Hexi Corridor into the North Foot of the Tianshan Mountains during 1761—1780, the relationship among migratory policy, the migratory peaks in the North Foot of the Tianshan Mountains and the extreme climate events in the Hexi Corridor were discussed. There are three migratory peaks which occurred in 1764—1766, 1772—1773 and 1777—1780. The migratory policy had not changed much during 1761—1780. The three migratory peaks were driven by the extreme drought climate events. There are three drought events occurred in 1763—1765, 1771 and 1775—1778. Migratory peaks lagged behind of the extreme drought climate events about 1~2 years. Among them, the third drought event pushed the last migratory peak, which made the Qing government change migratory policy in 1780. It was formed a complete chain of effects-feedback among the extreme drought climate event in the Hexi Corridor, the migratory peak in the North Foot of the Tianshan Mountains and the government′s migratory policy changes during 1775—1780.

extreme climate event; the North Foot of the Tianshan Mountains; migration; policy change; the Hexi Corridor