Based on the soil critical equilibrium theory, the paper discussed the distribution of earth pressure on retaining wall under the working conditions with or without excavation and backfilling between the wall and ground by thinlayer method, deducted the formulas of active earth pressure strength and coefficient of active earth pressure. The results show that the relation between the earth pressure strength and the depth of wall is linear under the working condition with excavation and backfilling and nonlinear under the working condition without excavation and backfilling between the wall and ground.