The separate and combined calculation of water-soil pressures on underground structures affects not only the design of supporting structures of excavations, but also the setting of uplift piles. Based on the field data, it has been proved to be reasonable to calculate the water-soil pressures by the separate calculation method for sandy soil. However, whether the combined calculations of the water-soil pressures is scientific or not for clay has been the focus dispute between geotechnical engineering and academic circles. In order to resolve this dispute, the author has proposed a calculation method to unify the separate and combined calculations of water-soil pressures. As a logically self-consistent theory, it carries out the transition between the two conventional calculation methods and provides a theoretical basis for the combined calculation method of water-soil pressures. This paper reviews the process of this theory initiation and further illustrates its rationality. Finally, it analyzed the value and development prospects of this theory.