Abstract: The Zhouqu event happened at 0∶12 of Aug.8, 2010 in Zhouqu County of Gansu Province of China. It is an oversize mountain torrent -debris flow disaster which brought about momentous casualty and loss of belongings. It is finished with Aug.30. There are 1467 death and 298 lost having been discovered in this disaster. It is calculated for that total volume of the solid deposits are 181×104m3 which rush out from Sanyanyu and Luojiayu gullies through grid calculation. The movement time from two mountains to Zhouqu County is separately 2.1 minutes for Sanyanyu and 4.3 minutes for Luojiayu on velocity calculation of the mountain torrent head in different sections in this disaster. The distances from two mountains to Zhouqu County are all about 2km in Sanyanyu and Luojiayu. The causes of formation about Zhouqu tragedy involved Sanyanyu being a debris flow gully of high frequency in history, the northern mountainous area producing strong potential energy impulsion, a rich of loosing rock or soil body in the gullies, rockmass loosing and cracking derived from many times of historical earthquakes, a long period of drought in this region since 2010 made in rock/soil body crack opening, the maximum rainfall to cause this calamity in the area at Aug.7, the mountain torrent-debris being of concealment in gestation, abruptness in happening and truculency in destruction, etc. Moreover, some buildings occupy and use partly the routeway in which a torrent-debris flows into Bailongjiang River in Zhouqu County in rapid urbanization.