Abstract: The characteristics and insufficiency of design indices of deflection of asphalt pavement in China are analyzed. The design indices to control the pavement deformation and rutting of flexible asphalt permanent are proposed. Based on the practical situation of China, the typical flexible asphalt pavement structures are adopted, and the mechanical parameters are analyzed by using the viscoelastic layered system for the U.S KENPAVE computer program. Through statistical regression by 1STOPT software a regression formula between theoretical deflection of pavement and radial stress of semi-rigid top surface is established. According to China's 2006 standard design formulae for deflection value, an equation for the radial stress of semi-rigid top surface of highway subgrade and top vertical stress is established. By comparing correlation coefficient check list, the credibility of the proposed design equation for flexible grassroots is validated.