The Yarkant River which originates from the Karakoram Mountains is the third Largest river in Xinjiang. The outburst floods often occurring in this river in recent years create hazards to human population, however, the problem about what makes the flood occur has not been solved yet.The purpose of this paper is to explore the major problems concerning the outburst floods.The first problem is to analyze the characteristics of these floods according to their basic features, their distribution in space and time, their situation of evolution, and the statistics of the flood peak and its magnitude.The second problem is that by comparing and analyzing the local meteorological information, the geomorphic condition and the features of these outburst floods, the idea is advanced that these outuburst floods are caused by discharge of the blocked lakes, not by torrential rains. They are different from the normal floods of glacial origin.The third problem is that with the help of air photograph taken in 1976 and the expedition for examining the traces of the floods in the Shaksgam valley, it is bound that the source of the floods is the Kyagar Thso lake blocked lake and Teram Kangri glacier located at the upper end of the Shaksgam vallay.A final problem is to point out that extent of the blocked lake is being reduced because the Kyagar glacier is declining, and to suggeste how to prevent this kind of floods.