Through coring without disturbing in lacuster of Angulinao L ak e, making thin sections with the core and observing under scanning electron micr oscope, annual lamina caused by winter monsoon is discovered. It’s the first rep ort on annual lamina in lake in semi-arid district which caused by monsoon.The lamina can play an important role in the research on sedimentology and environme nt evolution. Through coring without disturbing in lacuster of Angulinao L ak e, making thin sections with the core and observing under scanning electron micr oscope, annual lamina caused by winter monsoon is discovered. It’s the first rep ort on annual lamina in lake in semi-arid district which caused by monsoon. The lamina can play an important role in the research on sedimentology and environme nt evolution.