Abstract: The Fenghuang substation is located in the planning industrial area in northern Laibin city of Guangxi, occupying about 170 m×160 m in area. Landform there belongs to gentle slope on a karst monadnock covered with soil layer on the surface. Any unfavorable geology such as soil cave is not found during drilling and geophysical prospecting. But dozens of soil caves, 6.81caves/hm2 in density and 489 m2 in total subsiding area, are met in construction period. The development of this kind of soil cave is not only fast, but also comes into being later than surveying works, thus it is easily to be overlooked in the evaluation and leads to constructing accidents. In this paper, forming mechanism of soil cave subside is expounded from the point of geological structure, hydrogeology and hydrometeorology as well as human engineering activities. It is thought that the main reason of the occurrence of soil cave is rainwater infiltration and erosion when the underground peak forest and loose earth exposed after the surface silt-clay layer being cleared away. According to the forming mechanism of soil cave subside, comprehensive treatment method that including increasing drainage ditches and hardening construction site to cut off infiltration pass way of the rainwater is put forth. Furthermore, cyclopean concrete infilling is adopted for treating shallow subsidence, and HIP consolidation grouting is adopted for treating deep subsidence. All the above comprehensive treatment methods have obtained good effect.