To study the influence of the intercity railway shield tunnel underpassing the new and old bridge pile groups of existing expressway and determine the protection plan, the safe project route, allowable disturbance settlement limit of the bridge pile, bridge protection scheme, and deformation law of the GuangzhouFoshan intercity underpassing the FoshanKaiping highspeed bridge piles are analyzed using deformation inversion analysis, allowable deformation back analysis, threedimensional numerical simulation analysis, and field verification, thus providing rational scheme. The results show the following. (1) A comprehensive protection scheme of "selecting the vertical safety line of route + compensation jacking + microdisturbance tunneling of shield + compensation grouting behind segment" is adopted to guarantee the underpassing of shield tunnel. (2) The allowable disturbance value of bridge pile can be obtained by finite element analysis, and can predict the deformation of the bridge pile when shield underpassing, thus providing monitoring and control indices for safe shield underpass. (3) The strengthened parameter control of shield and dynamic monitoring on bridge piles are carried out, resulting in small bridge pile settlement within 2 mm.