Abstract: 14 outburst floods had been occurred in Si Keshu River since 1970. The floods occurred in winter ( 22 November to 22 . December). The flood Peak with rising and dropping steeply was bigger than that of occurred in summer. The outburst floods may be caused by the water releasing of the river ice-dammed lake in middle of the river. There were several places where can be easy formed Ice-dammed lake in Si Keshu River Valley. The formation of the ice-dammed lake was related to both the river Landform and temperature fluctuation.