In the present paper we improve the method to calculate socketed depth of large diameter soft rock socketed piles in water project, and explore the relationship between the socketed depth and influencing parameters. Assuming that the rock resistance of rock-socketed pile side is linear distributed and the rock failure criteria matches with the two parabolic Mohr criterions, it is possible to derive the rock-socketed pile’s calculation model on the basis of rock-socketed pile subjected to normal stress and tangential shear stress. Hence, the minimum depth analytical solution can be given by hydrostatic equilibrium. By using a laboratory model test and a practical project to verify the method, results show that: socket length increases with the increase of the horizontal force and continuously decreases with the increase of the pile diameter and rock uniaxial compressive strength. However, when the rock uniaxial compressive strength increases to a certain value, the rock-socketed depth shows a slight decreasing trend. Additionally, the overburden pressure has little effect on the rock-socketed depth.