Abstract: The monitoring of the deformation of surrounding rock was one of the most important contents in underground construction project.How to improve the current monitoring instruments and obtain the closest value to the actual deformation information of the surrounding rock was an interesting problem of many engineers.The monitoring principles and structure of the spigot coaxial rod extensometer(SCRE for short) were introduced.Likewise,the monitored data of theoretical conversion formula were given.On the basis of actual measurements,analysis of tunnel construction and the monitored deformation infomation of the surrounding rock,the deformation regularity of surrounding rock after the excavation of cavern was disclosed,and the optimum support time and construction method were determined.The proposed method could be employed to predict geological disasters such as large deformation and to provide basis to the information-based construction.