Abstract: The horizontal slice element method for calculating the passive earth pressure against rigid retaining walls is extended to cohesive backfill. The formula of the nonlinear distribution of passive earth pressure is derived to satisfy the reciprocal theorem of shear stress. According to the Mohr-Coulomb theory, the lateral passive earth pressure coefficient can be determined, and a simplified expression of the total passive force is obtained. The influence of the shear stress increment between soil strips on the passive earth pressure is discussed by two calculation models. The results are compared with the existing classical theory. The comparison shows that the formula in this paper degenerates to the Rankine formula when there is no uniformly distributed load. If the backfill is cohesionless soil, the results are consistent with those in the literature that considered the soil arching effect. The calculated results are also consistent with the existing experimental results.