Research methods: Based on the elastic and plastic theory, the stress distribution of soil cave in foundation can be deduced in karst region. With the action of self-weight stress of soil mass and additional contact pressure, the stress concentration will be taken place in soil mass around soil cave periphery. By the Mohr-Coulomb yield criteria, whether the soil mass around soil cave is destroyed can be determined. When subgrade bearing capacity is calculated according to the item 5.2.5 of “Code for design of building foundation" GB 50007-2002, it should assured simultaneously that the soil mass around soil cave cannot be had the plastic failure, and the P value of contact allowable pressure can be obtained, the less value between fa and P is the subgrade bearing capacity for soil cave.