Abstract: Aiming at foundation pits (of impervious aquiclude) with confined underground water in soft soil area, calculation model for piping based on plastic deformation failure is developed from piping mechanism of soil under foundation pits, and the concept of yield stress ratio & judgement standard of piping for foundation pits are presented. Calculation results of examples were compared with results of centrifuge test, field observation and pressure balance method. The results show that, the calculation results of the model agreed well with the results of the test and the field observation, but the results of the pressure balance method were not consistent with the results of the test and the field observation. Therefore, it is rational to adopt the model of piping based on plastic failure for foundation pits (of impervious aquiclude) with confined underground water.