Abstract: The original equilibrium state of underlying mined-out area is surely to be broken by the approaching construction of highway tunnels, and it will cause stress redistribution. In order to study the influence law of underlying mined-out areas with different dip angles on tunnel construction stability, it used finite element software to build a calculation model of tunnel in mined-out layer, carried out a numerical simulation, studied the influence law of underlying mined-out area with different dip angles on displacements around tunnel periphery, inner force of primary support and the plastic zone. The calculations indicate that the displacement around tunnel periphery increases with the decrease of dip angles of underlying mined-out areas; the distribution discreteness of inner force of primary support increases due to the mined-out area, the axial force of crown is largely influenced by this and characterized by the decreasing of axial force which has a verse relationship with the dip angle; the plastic zone of surrounding rock enlarges, even penetrates through the caving zone of mined-out area and has a verse relationship with the dip angle. Thus the smaller the angle of underlying mined-out area, the higher the construction risk, the worse the stability of surrounding rock and the more unfavorable regarding force applied on structure, which makes it necessary to take effective measures to improve the treatment for underlying mined-out areas.