Abstract: Extensive research and investigations on the durability of existing railway and highway tunnels indicate that the majority of tunnels suffered from various degrees of defects induced by durability deficiencies. There are many reasons that can contribute to the lack of durability of the major structure of a tunnel and the root cause proves to be the philosophy of design. The previous design standards of mountain tunnels were generally alow level and did not sufficiently consider tunnel structure durability, which could only be regarded as strength-oriented design rather than comprehensive performance-based design. Many misconceptions involved in the philosophy of tunnel design include failing to pay sufficient attention to the geological and hydrological conditions, inappropriate concrete material, failing to strictly control the initial cracking of concrete, single composition and poor gradation of the cementitious material, thicker second linings with excessive stiffness and poor toughness, etc. Regarding the design deficiencies in the structure durability of mountain tunnels, the following main measures are proposed: multiple composite cementitious material is to be used to prepare concrete, composite cementitious material is distributed by the batching plant, the primary support is to be strengthened while the second lining thickness is reduced, and proper fiber is to be added to the concrete.