Abstract: Soil work refers to the soil construction of foundation engineering of Chinese ancient buildings. To effectively protect Chinese ancient buildings, the foundations in the Forbidden City were taken as examples, their soil work techniques were studied by means of site investigation as well as literature analysis. Details such as the constitution of soil foundation, groundwater treatment, application of cementing material and so on were discussed. The results show that the foundations of the buildings in the Forbidden City were made up of alternative layers of brick blocks and lime-soil, or layers of lime-soil, both of which included complicated and strictly construction processes; to deal with groundwater, vertical timber piles and layers of gravels were used; cementing material such as lime, glutinous rice, tung oil, alumen had been found in the soil, which could benefit the strength, bonding performance and waterproof property of the foundation. Besides, the official codes of Yingzaofashi the in Song dynasty and the rules of Gongchengzuofa in the Qing dynasty played important roles in the soil work of the buildings in the Forbidden City.