Abstract: Based on the ponding loading test of Gannan 330kv transformer substation's foundation, the collapsible mechanics of gravel, soil is analyzed by the structure theory of soil's collapsible deformation and the main factors of gravel soil's collapsible distortion. And it's pointed out that the collapsibility is mainly due to the special structure of gravel soils which including big grain framework structure and granule cementation which filled in the big space. Because of gravel soil's main framwork's compressive and shear strenth decreased, the stucture of it is damaged too. Then the second collapsiblity come into being.