Abstract: The fundamental behavior of rock mass can be drastically changed when submerged in water. It is alsovalid for the rheological behavior of rock mass. In this paper, the time-dependent stability thery is discussedhased on the changes of fundamental prperties before and after the rock mass iS submerged in water. Therheological instability criterium is estublished for submerged rock mass and several cases of slope sliding dur-ing rain season are analysed in this peper.