Abstract: In order to reveal the water outburst mechanism of Karst collapse pillars (KCP) and provide theoretical ba- sis for the water outburst prevention,based on the dual-porosity media seepage theory,the authors consider KCPs as three main components,i. e. solid matrix,fluid and filling material in fractures between matrix,then a mechanical mod- el for KCP water outburst involving the processes of solid deformation,water flow,particles erosion and migration,frac- ture and the permeability change were presented. The seepage characteristics of KCPs were investigated by numerical simulation based on engineering practice,obtaining the variation of porosity,seepage velocity,water pressure,particles concentration as well as water inflow volume as the time. The research results indicate that ① the water inflow of KCP obtained by numerical simulation is agreed with the field test data,which indicates the correctness of the mechanical model. ② the particles in KCPs will be eroded and transported under the coupling effect of deformation-seepage-ero- sion,fractures will increase rapidly,then several main seepage channels will form and eventually cause the KCP water outburst accident.