Research methods: The analysis is made with the theory for structural design of flexible pavement and a new computing method for surface course thickness of flexible pavement is put forward with large deflection theory of slab. According to the real load distribution of wheel pressure, the wheel pressure is assumed as equivalent rectangle distribution instead of circular distribution used by traditional method. According to the deformation features of road slab, the simply supported boundary condition with long side is applied. The structural calculation is made with simplified model for infinite slab, from which the formula is derived for calculation of surface course thickness based on the large-deflection elastic theory. The calculator program is programmed and analysis is made for concrete calculation example.