The dangerous zones of surrounding soil which are not in plastic state cannot be effectively divided during foundation pit excavation. Hence, the yield approach index (YAI) is used to evaluate the regional safety of the foundation pit. The computing program is compiled based on language fish and solved by software FLAC3D. And then the results obtained are compared with plastic zone distribution obtained by finite difference method and the results of vertical displacement of rock and soil. Finally, the safety state of surrounding soils of foundation pit is calculated based on the concept of YAI; and the distribution and variation tendency of YAI of surrounding soil during foundation pit excavation are obtained. The results show that the YAI method can effectively express the calculation results of finite difference method, on the basis of which the YAI of nonplastic zone can be solved and the dangerous zone of foundation pit can be effectively divided. The results can provide reference for safety evaluation of foundation pit.