The rheological behavior of adjacent rock is one of the important factors that influence the deformation and long-term stability of underground cavern. Under long-term load，the rheological behavior of rock mass occurred，and the rheological phenomenon of weak intercalation becomees more obvious. As an engineering example，a large-scale underground cavern of hydropower station is studied

in which there are reciprocal chiasmata with several weak intercalations. Based on the visicoelasto-plastic rheological model of rock，the rheological characters of the surrounding rock mass are simulated by using FLAC3D software. Through the analyzing of the calculated results，the long-term stability of underground cavern is estimated by studying displacement，displacement velocity，stress and plastic zone. The results show that the rheological effect of underground cavern is very remarkable. As for several weak intercalations are adjacent to the underground cavern，the deformation of intercross between cavern and weak intercalations is large

which has someing influence on the long-term stability of underground cavern. It is very important to consider rheological effect for long-term stability estimation of underground cavern.