Abstract: After analyzing of the high and low level circulation configuration of the days of 40 general gales and 20 disastrous gales from 2007 to 2010 in Xiluodu hydroelectric dam and taking the background of the gales weather system into consideration,the gales in Xiluodu hydroelectric dam can be divided into 6 categories of Low-pressure (Southwest Low-pressure),Cold-front & Cold wave (Cold high diffusion), Low Vortex & Shear,Westerly Slot,Low-level jet (LLJ) and Subtropical.The focus of various types of the gales forecast has been extracted from it and the formation mechanism has been analyzed.A reference to forecasters has provided to improve their ability of gales forecasting and early warning in the Xiluodu hydroelectric dam,to ensure the safety of the personnel and equipment in the construction period and the quality of the project,to reduce the risk and cost savings in the Xiluodu dam.The findings show that the daily influence of gales on weather system in Xiluodu dam is not single, but a variety of influence systems coexist,especially the disastrous gales,which are of more complicated influence system.Its formation mechanism can be divided into ground systems directly affecting type,west winds driving the transmission type and high-altitude power unstable type.