The longitudinal reinforced earth-rock fill dam has the advantages of low cost and high construction efficiency, which is especially favorable for the reconstruction of old or diseased dams, and for the medium and small dams built in the areas lacking qualified clay materials. Due to the lack of design experience and referential precedents, the new-type dam needs to be discussed in depth in the aspects of seepage stability, stress and deformation of the longitudinal reinforced core wall, and the dam slope stability. The finite element method and finite difference method were used to analyze the stability of the model based on Fangtianba Reservoir, which is the first project adopting this new scheme in China. Meanwhile, the optimization of dam slope gradient of this new-type dam were discussed. The results showed that the seepage prevention effect of this new-type dam is superior, and compressive stress is the major stress on the concrete core wall, and there is less possibility of structural failure. The slope gradient can be optimized theoretically, but needs to be tested by long-term engineering practice. The longitudinal reinforced earth-rock fill dam is stable in the case of the low dam height, reasonable slope gradient and guaranteed construction quality.