An elastoplastic constitutive model based on Zienkiewicz-Pande yield criterion is developed secondarily in FLAC3D and applied to stability analysis of surrounding rock during the process of excavation in a certain underground hydropower station. Zienkiewicz-Pande yield criterion is the one of forms of improved Mohr-Coulomb criterion，which is a smooth curve and has neither the singular vertex in the p-q plane nor the ridge corners in the π-plane. It is easy to handle not only in the numerical iterative calculation process

but also taking into account the relationship between yield curve and the hydrostatic pressure to some extent

as well as the impact role of the intermediate principal stress ? 2 on the yield surface. The criterion has been applied to calculation for excavation and supporting in several large-scale underground caverns of hydropower stations

but has not been adopted by any large numerical software. According to elastoplastic mechanics

incremental iterative calculation format of elastoplastic constitutive model on Zienkiewicz-Pande yield criterion is derived in detail. Based on the program interface of secondary development provided by FLAC3D

VC + + programming language is used to realize the calculation process and compile into dynamic-link library files loaded and invoked. In simulating to an ideal circular tunnel

the self-defined model is consistent with Mohr-Coulomb criterion to verify the correctness of the calculation format. Finally

this constitutive model is applied to stability analysis for excavated surrounding rock in large-scale underground caverns; and the distribution rules of calculated plastic zone

displacement field

stress field are accord with Mohr-Coulomb criterion

which validates the applicability and reliability of the model further.