Combining with a three-dimensional numerical model for a TBM tunnel of Lanzhou water supply project, the tunnel excavation process is simulated with finite difference method and the Mohr-Coulomb failure criterion to estimate the support installation time. Based on the convergence-confinement method, the deformation tendency of the monitoring section can be analyzed during the tunnel advancing. It is shown that the regularity of longitudinal displacement is related to the surrounding rock quality. The modified formula of longitudinal deformation curve can be fitted by the change regularity. With the method of virtual supporting force, the tunnel excavation can be assumed as an instantaneous progress in unique step to analyze the regularity between the deformation of surrounding rock and the excavation load releasing ratio. And the advance distance could be correlated to the excavation load releasing ratio with the same displacement completion ratio. So the supporting installation location away from the tunnel advance face can be determined by the excavation load releasing ratio when the deformation increases abruptly. The results show that the related parameters in the modified formula are convenient to be determined and satisfied with the fitting features. And the recommended supporting installation locations meet well with the common sense.