Abstract: In the project of passenger dedicated Line from Beijing to Shijiazhuang,a 5 km long tunnel parallel to the existing Beijing to Guangzhou Railway Line with a distance ranging from 5 m to 20 m was built with open excavation method.The longtime and continuous dynamic load caused by running trains would necessarily influence stability of tunnel supporting structure.So it was vital to establish the reasonable locking force value of anchor based on study on response law of anchor force.Thereby a site test was designed on a standard tunnel section and performed to measure anchor force for half a year.Meanwhile a digital model was made with FLAC-3D according to site condition and construction steps to analyse the law.The research showed there existed a critical value of locking force.Bigger than that,the supporting structure would be stable and the fluctuation of anchor force would not cause obvious stable problem.Smaller than that,the supporting structure was sensitive to dynamic load.Under the condition,the displacement of anchor head satisfied parabola function with locking force.The relative variation range of dynamic stress rised in line with power function with increase of vibration strength and decrease of distance of train.The test data partly proved the foregoing conclusions.