To ensure the stability of surrounding rock, the 3D finite element model of Houci tunnel expansion project on ZhangzhouLongyan highway is established and ground surface settlement, vault subsidence, surrounding rock displacement and variation of stress on tunnel arch feet and crown are analyzed. The calculation results show that: 1) The tunnel displacement law of expansion is different from that of new tunnel construction, and the tunnel displacement curves of expansion shows obvious asymmetry. 2) The deformation speed of the unstable section, 12 m in front of and 24 m behind tunnel working face, is large. 3) The displacement formulas for expansion tunnel, which can predict the deformation of Houci tunnel, is proposed. 4) The tunnel arch feet show a stress concentration trend. The principle stress of tunnel arch feet increases and that of tunnel invert decreases as the excavation goes on. The stress of tunnel vault develops into small tensile stress in the end.