Abstract: Three-dimensional slope stability analysis methods and the search for the critical slip surface in three dimensions have always been hotspots in the field of slope engineering. Egg-shaped slip surface slope stability analysis methods and the search for the critical slip surface based on unified strength is carried out. By embedding the unified strength into the three-dimensional slope stability analysis method for constructing the normal stress over the slip surface, a three-dimensional slope stability analysis method based on unified strength is established. Assuming that the three-dimensional slip surface is egg-shaped, the egg-shaped slip surface equation is constructed, and the particle swarm optimization algorithm is adopted to realize the search for the critical slip surface of the three-dimensional slope. The rationality of the method is verified by examples. The results show that the safety factor based on unified strength is higher than that based on Mohr-Coulomb strength, and the increase is positively correlated with the <italic>b</italic> value, with the maximum increase reaching 20.63%; the shape of the critical egg-shaped slip surface is unaffected by the two strength criteria; the safety factor of the egg-shaped slip surface is 0.24% to 5.00% lower than that of the ellipsoidal slip surface. This method has demonstrated remarkable efficacy in practical engineering applications. The method not only enrich the three-dimensional limit equilibrium method but also provide a reference for similar projects.