In practice, most of the natural slope instability is induced by a decrease in the strengths of the local soils. Therefore, the local strength reduction method is more reasonable than the traditional strength reduction method, because it only reduces the regional soil strengths near the sliding surface, and the strengths of other soil elements remain unchanged. However, for the selection of the local reduction range, the local strength reduction method is affected by subjective factors and lacks objective standards. Therefore, the parallel–local strength reduction method, which is based on the idea of the local strength reduction method, is proposed here. First, the finite-element limit equilibrium method is used to determine the shape and location of the sliding surface; next, the yielding approach index is used to calculate the yield region of the slope. Finally, taking the boundary points of the yield region that are located in the slope toe as the starting points, the local reduction area boundaries are determined by drawing the parallel curves of the sliding surface. The example shows that the proposed method is feasible and rational.