Abstract: This paper presents and analyses the long term prototype observational data of some large underground hydro-powerhouse in China. The analysis shows that in both the distribution and the magnitude of stresses, there exists a great difference between the value measured in prototype and the value designed by Protodyakonov's theory. All the reinforcement bar stresses measured in lined top-arch represent some time-effect, i.e. these stresses increase steadily and slowly with the time elapsed. A visco-elastic model of K-H in series is used by authors to analyse the rock pressure acting on a lined top-arch. In addition, some opinions for improving the design and construction of lined top-arch are suggested.