The longitudinal reinforced earth-rock dam was a new type of dam, the dam structure was formed by setting the rigid impermeable core wall in earth-rock dam, that the rigid core-wall played an important role in anti-seepage bearing water and soil pressure and resistance to deformation. The dam was divided into the upstream side and the downstream side by rigid core-wall, and the displacement of the wall and the water and soil load born by the wall changed with the water level on the upstream side, A transition between active and passive stress states was unlocked in the driven area of the upper and lower dam, which was segregated by rigid wall. Based on the Coulomb earth pressure theory and the safety definition of rigid core-wall bearing load that was proposed in this paper, the safety of rigid core-wall as the retaining wall bearing water and soil pressure was analyzed under three conditions of completion normal water storage and sudden drawdown of water level, and the analytic formula of safety in the three conditions were provided. On this basis, according the relation between the wall safety and the dam stability the calculation method of the reduced coefficient of passive earth pressure was proposed, the calculation method considered the role that the rigid core-wall bored bidirectional water and soil pressure front and behind dam. The result showed that the stress conditions deformation and stability of the wall and the dam stability interrelated. The passive earth pressure loaded in the wall be unlocked with the increase of active pressure under normal water storage condition, and the coefficient of passive earth pressure was bigger than the other two conditions. The coefficient of passive earth pressure obtained by the calculation method in this paper was secure, and the section of dam could be optimized.
