Abstract: A sudden snowmeltrainfall mixed flood with high flood peak and big volume occurred in all the distributaries of the Ertix River Basin on June 1, 2005. In which the flood occurred in the Kuyertes River, a headstream of the Ertix River, was the maximum recorded since recent 50 years, and the 2nd and 3rd maximum floods in the records occurred in the Burqin River and Haba River separately. The flood resulted in a huge economic loss in the local area. In this paper, the causes, process and characteristics of the flood were analyzed based on the observed data of flood, rainfall, temperature and atmospheric circulation pattern. The results were as followings: (1) Previous temperature and largescale precipitation played an important role in the formation process of the snowmeltprecipitation mixed flood in the Ertix River Basin; (2) Temperature change, 0 ℃layer height and precipitation were necessary for accurately predicting flood trend. The 4th basinwide flood recorded since recent more than 50 years occurred under global warming and the obvious increase of snowfall in the Altay region in winter, and the possibility of occurring disastrous flood would be increased; (3) Duration of snowmeltrainfall mixed flood is long, the flood peak is high, and the sandcarrying capability of such flood is strong, so these problems should be paid great attention to in designing the projects of urban flood prevention and control and water storage; (4) Construction of prewarning system of flood prevention and control should be enhanced, especially along the mountainous rivers if there are large cities or important projects downstream so as to decrease the losses caused by disastrous flood.

Key words: snowmelt-rainfall mixed flood, silt content, the Ertix River, Xinjiang