Large-scale concrete-face rockfill dams are facing with technological challenges caused by geological condition, high seismic intensity, and large dam height. We adopted the limit equilibrium theory and reliability theory to calculate the dam slope stability of Kajiwa concrete-face high rockfill dam. We analyzed the slope stability and reliability considering nonlinear strength parameters, and investigated the influence of technical indexes and safety factors on the slope stability. Compared with the limit equilibrium method, the reliability-theory-based method employed to design dam slope could quantify the safety margin, and thereby is contributive for the optimal design of high rockfill dam slope. It’s of practical significance for cost reduction and environmental protection.