By analyzing and studying the projects of bridge shield method undercrossing subgrade, the key influencing factors on the deformation of bridge shield method undercrossing subgrade are summarized, and the deformation mechanism is deeply analyzed. According to the proposed key influencing factors and relying on the actual project, the design application of bridge shield method undercrossing the existing expressways and structures is carried out. A variety of designs to control the deformation of existing subgrade and structure is proposed.