In order to study reasonable secondary lining supporting parameters, the Tiefodian 1 tunnel of Baoji-Hanzhong expressway in Shaanxi province is taken as an example. The numerical calculation model was established by MIDAS software to analyze the secondary lining in deep buried three lanes tunnel under grade Ⅳ and Ⅴ. And the safety factors of different secondary lining thicknesses were calculated. The results show that tunnel structure safety factor will meet the specification requirements when the second lining thickness of grade Ⅳ optimizes to the 75% design value and grade Ⅴ optimizes to the 80% design value. It is concluded that the current provisions of the secondary lining thickness in Code for Design of Road Tunnel are conservative. The secondary lining thickness can be further thinning for the general situation of tunnel design.