The unified theory of the four fundamental forces has been a goal pursued tirelessly by physicists. Attempts have been made from various aspects such as quantum field theory, general relativity, and string theory, but none have yielded satisfactory results. This article starts with the electric field interaction between two charges. By considering the additional effect of positive and negative vacuum polarization charge clouds around the particles, the divergence equation of the electric field can not only derive the expression of the potential energy of the non-divergent electric field at zero distance, but also derive the potential energy expressions of the non-divergent nuclear force, short-range weak force, and universal gravity. These four forces are different manifestations of the static electric force between charges, and all have a non-zero equilibrium distance. The well-known Newtonian universal gravity, Coulomb force, and Yukawa nuclear force are all results when the action distance is much greater than the equilibrium distance.