The annular excavation with core soil method used in Shanziding Highway Tunnel can not guarantee successful tunnel construction in weak surrounding rock, so the expanding lining method is put forward. First, construction sequences of expanding lining method are discussed; and then, ANSYS finite element method is adopted to establish 3D computational models for expanding lining with thicknesses of 0, 20, 30, 40, 50 cm and 60cm; finally, mechanical behaviors of expanding lining and primary support are analyzed. It is concluded that expanding lining is a relatively superior method for tunnel construction in weak surrounding rock; and when thickness of expanding lining reaches 60 cm, principal compressive stress and tensile stress of primary support are 16.4 MPa and 0.486 03 MPa respectively, which can meet the material request.