The influence of the distribution of the initial normal stress on the stability of slope was investigated using the explicit solution of slope safety factor based on modification of normal stress distribution over the slip surface. The initial normal stress distribution over the slip surface was assumed and then modified by a correction function with undetermined parameters so the slip mass can satisfy the equilibrium conditions of force and moment in all directions. An equation satisfying all the equilibrium conditions was derived, and the safety factor was calculated. Slope stability was also evaluated. Computation results show the minimal influence of different distributions of initial normal stress on the 3D symmetrical slope. The maximum difference in the safety factor is below 5%. For the common slope, the influence is relatively large and the difference in the safety factor is 6.2%. The maximum difference compared with the other methods is 28.7%. Therefore, verifying the rationality of normal stress distribution over the sliding surface is necessary in engineering practice.