In order to solve the differential settlement of soft subgrade in coastal areas，based on the elastic deformation theory of overconsolidation stress ratio，the calculation and analysis of artificial overconsolidation stress ratio and the new technology of lightweight replacement were carried out to reduce the additional stress of vehicle load and structure weigh.The results show that the replacement thickness of the lightweight material with suitable density can make the additional stress at the bottom of the subgrade less than the deadweight stress of the original soft soil，and the additional stress is less than the initial flow stress of the soft soil.The resulting overconsolidation stress ratio can put the soft soil in a state of elastic deformation.The observed data of settlement performance of the test road show that the settlement of the pavement structure remains with lightweight replacement is stable at about 1 mm one year after construction；the settlement of conventional pavement structure reaches 17 mm，which exceeds the upper limit of driving comfort of 15 mm，and the settlement is still intensifying.The proposed lightweight replacement technology based on the artificial overconsolidation stress ratio theory can effectively solve the differential settlement of soft subgrade，which has significant theoretical value and practical application prospects.