Abstract: A deep excavation is a three-dimensional space structure system which has length and width as well as depth. Usually, it is taken as a two-dimension plane strain problem in the current design code. Consequently, the three–dimensional character and size effect cannot be reflected clearly. To improve this, the concept of a soil pressure utilization factor is proposed and the calculation method of the factor is established based on the elastic resistance method. First, the form of horizontal displacement curve of the top beam on a cantilever retaining structure is assumed to be similar as that of a simple beam under distributed load. On this basis, the soil pressure utilization factor, the deformation of the retaining structure and the spatial distribution of internal forces on the cantilever retaining structure in a deep excavation are calculated. Engineering examples show that the foundation pit deformation in considering the spatial effect of soil pressure is consistent with the results measured practically.