Abstract: Due to the green and environmental protection operation mode, the tram is leading the transportation industry into sustainable development in China. According to the structural characteristics and engineering properties of soft soil foundation in Nanjing, a vacuum preloading combining mixing pile foundation treatment method is proposed. Based on the monitoring results of surface settlement, layered settlement, horizontal displacement and pore pressure in construction period and cumulative settlement in operation period, the improvement effect of the proposed method as analyzed. It is shown that the pore water pressure gradually decreases with the increase of the depth. The horizontal displacement and layered settlement all decrease gradually during the process of vacuum. The total surface settlement remains unchanged after vacuum preloading of the soft soil foundation for 2 months, which means that the consolidation of soft soil is approximately completed. The total settlement at the surface of the subsoil is approximately 440 mm. The cumulative settlement after construction is 4.2 mm in half a year and approximately 9.8 mm in 10 years by the predicted method, which satisfies the requirements of the settlement control. It is concluded that the method of vacuum preloading combining mixing pile can significantly improve the tram soft soil foundation.