To address the application of an ultra-thin wearing course in expressway asphalt pavement maintenance engineering，the ultra-thin wearing course system based on the balance design concept was systematically studied.In this paper，the action mechanism and application characteristics of modifiers were analyzed，and the proportion design test of the ultra-thin wearing course was designed based on the balance design method.Finally，according to the proportion design test，the optimal proportion of the ultra-thin wearing course material was selected for test road paving.Research shows that the direct-cast high viscosity modifier is convenient for transportation and storage，improves the elastic recovery of asphalt mixtures and reduces permanent deformation.Under the condition of good gradation and intercalation，a reasonable increase in asphalt dosage can effectively improve the high-temperature stability，low-temperature crack resistance，and water stability of the ultra-thin wearing course asphalt mixture.With the increase in modifier content，the high-temperature stability of the asphalt mixture is gradually improved，which reaches the optimum when the asphalt content is 6.8% and the modifier content is 0.9%.Considering the performance and economic factors of the asphalt mixture，the best material ratio of the ultra-thin wearing course is determined and successfully applied to the test road of an expressway maintenance project.The test results show that the ultra-thin wearing course provides good water tightness，anti-sliding performance，and noise reduction performance.