Abstract: Twenty sites of soil landslides and soil creeping and deformational masses as the main sources of loose deposits are developed in the Heigou gully,Lengqi,Luding,Sichuan.In general,these soil landslides and soil creeping and deformational masses have smaller scales,slower velocity and loose structures,and therefore they are prone to be sweeped away by floods in the gully rather than result in the formation of barrier lakes and extraordinarily serious debris flows calamities.The present paper gives careful calculations of the maximum debris flows in the Heigou gully in July 2006,the extraordinarily serious debris flow calamities in the last sixty years,with a calculated flow velocity of 3.47 m/s and maximum rate of discharge of 122.79 m³/s.