In order to determine the effective soil thickness for the greening of urban relocation sites, soil thickness of urban relocation sites was defined based on the basic concepts of soil, miscellaneous fill, construction waste and soil by comparing the differences between urban relocation and traditional agricultural soils; Based on the depth of the construction waste layer and the relevant standards for landscaping planting soil, the connotation of the effective soil thickness was defined for urban relocation sites, and Shanghai World Expo Cultural Park and Shanghai Sanlin Valley were taken as study examples of urban relocation sites. The results showed that the soil thickness of the urban relocation site is the sum of the thickness of all soil layers in soil profile in the urban relocation site; the effective thickness of the urban relocation site greening is the thickness of soil layer or after improvement which physiochemical properties are in line with the local standards for landscaping planting soil above the groundwater in the urban relocation site. Before the completion of the Shanghai World Expo Cultural Park, the soil thickness of the urban relocation site was 2.4-4.5 m. However, because soil physiochemical properties did not meet the standards of requirements for landscaping use, the effective soil thickness was zero, and extraneous soil had to be used for landscaping use. Before the completion of Shanghai Sanlin Valley, soil thickness of the urban relocation site was greater than 1 m, and soil could be used as landscaping planting soil after improving, but the effective soil thickness for greening was 1 m due to the existence of the groundwater layer. Therefore, the established method in this paper for dividing the effective soil thickness of urban relocation land greening can provide a scientific basis for the rapid estimation of the amount of in-situ soil and guest soil.