In order to analyze the influence of construction of new interchange tunnel on existing tunnel, a three-dimension model test of interchange tunnel is carried out with the system of structure and surrounding rockmass of highway tunnel. Existing tunnel’s surrounding rock pressure, internal displacement and supporting internal force are measured. The results show that, firstly, excavating new tunnel has obvious influence on section Ⅰ of existing tunnel, and has little influence on section Ⅱ.All surrounding rock pressure keeps decreasing and arch bottom surrounding rock’s stability reduces. Secondly, crown and hance internal displacement manifest tensile deformation, and the deformation at crown is bigger than that at hance. Thirdly, exiting tunnel’s supporting axial force keeps increasing and supporting moment keeps decreasing. Finally, excavating new interchange tunnel has obvious influence on exiting tunnel’s surrounding rock pressure, internal displacement and supporting internal force when adjacent space is 0.25D, and it indicates that interchange tunnel’s adjacent space should be no less than 0.5D.