In order to study the active earth pressure of the finite soil behind the retaining wall, the trace of small principal stress is simplified from circular arc to inclined straight line, and the soil behind the retaining wall is divided into several inclined straight thin layer elements. In view of the limit equilibrium condition of the layered soil behind the retaining wall, a method for calculating the active earth pressure of the finite soil retaining wall is proposed, and the theoretical expression of the active earth pressure force and the height of the applied point is given. Finally, the correctness and rationality of the method are verified by comparison with an example.