This paper aims to develop a new prediction method of rock mass stability, which is useful in a multi-step excavation such as cavern construction, based on the results of back analysis to model out inhomogeneous rock mass behaviors during excavation. Assuming the Duncan-Chang non-linear elastic relationship for rock masses, its parameters can be determined from the results of back analysis applied during excavation and strains at the stage of further excavation can be properly estimated so as to assess rock mass stability. This method is applied to the actual cavern construction problem and the results suggest that this indicates an excellent capability to predict more reasonable strains for further excavation steps at the early stage of cavern excavation such as an arch portion.