Based on the beam theory of elastic foundation, an approximate analytical algorithm has been proposed for the displacement-load relationship of anchor plates in cohesive soil with appropriate assumptions. Then, based on the numerical simulation results of the displacement-load relationship of six square anchor plates of different sizes, two fitting parameters can be obtained of the relationship between the horizontal foundation coefficient of soil and the horizontal displacement of the anchor plates. The feasibility of the theoretical analysis method is verified by the field test results of the anchor plate pulling force. Finally, an inquiry is made into the influence of soil cohesion and internal friction angle on the pulling capacity of anchor plates. The results verifies the feasibility of the approximate analytical algorithm for displacement-load relation of square anchor plates in a certain depth range.