Abstract: Some ideas about the active earth pressure coefficient Ka of retaining Wall for Coulumb's theory,Rankine's theory and the appendix of "Building Code of Foundation Design GBJ789" are proposed. The calculating method of active earth pressure is improved. The method to determine the retaining wall section by the condition of anti-slide stability and an experimental formula of antioverturn stability are given. The calculations of wall strength and foundation stress are expounded, and an example of calculation is given.