Abstract: The tunnel rock mass has a complex stress state. It is important for tunnel rock mass stability analysis that the rock mass failure region distribution during construction is evaluated appropriately. The yield approach index is proposed in the paper to evaluate the rock mass failure extent, which is suitable for the rock mass stress failure probability under complex stress state. The Mohr-Coulomb type rockmass material is used in the paper to deduce corresponding calculation equations for yield approach index. The numerical method for the calculation of yield approach index is implemented in nonlinear finite element software user subroutine. In the Ganzhou-Longyan mongline railway tunnel construction process between DKl33+095 and DKl38+237, the wet-sprayed fiber reinforced concrete lining structure is used as the first stage lining structural and the step tunnel excavation lining construction process is used. To evaluate the tunnel rock mass failure zone evolution during tunnel construction, the nonlinear finite element analysis with consideration of rock mass yield approach index is performed for the railway tunnel first stage lining construction process using the wet-sprayed fiber reinforced concrete lining structure. The rock mass failure index evolution during construction process is analyzed and the tunnel rock mass stability is determined during step tunnel excavation lining construction process. The numerical result shows that the rock mass failure zone mainly exists during the bottom step construction process. The yield approach index for rock mass failure estimation provides more information than that of common rock mass plastic zone distribution. This index is useful for the engineers to evaluate the tunnel excavation and lining plan quantitatively.