Abstract: In order to matching design the stiffness of composite auxiliary spring, the structure of the main-auxiliary spring assembly structure, which includes a composite auxiliary spring, was designed. The equivalent load of the composite auxiliary spring was calculated by the concentrated load method. According to the change of the deflection of the original steel leaf spring, the equivalent stiffness of the composite auxiliary spring was estimated. The equivalent stiffness of the composite auxiliary spring was matching designed according to the design theory of steel leaf spring. The finite element simulation for the total stiffness of the main-auxiliary spring assembly was made by ABAQUS software. By adjusting the ply number of the composite auxiliary spring, the equivalent stiffness of the composite auxiliary spring was modified. The proposed matching design method processes great importance for the popularization and application of composite leaf spring.