Abstract: According to the parameter perturbation theory，a combination of the ns wave functions of two hydrogen-like atoms with effective nuclear charge number of Z* = 2-σ is chosen to be the first order approximation and the fourth order approximation of wave function for the ground state of helium atom. The fourth level approximate energy of the ground state of helium atom is calculated by using the application of perturbation method. The calculation results show that the error of the fourth level approximation energy of helium atomic ground state by the parameter perturbation method is ΔE= 0.004922028*e^_s2/a₀ comparing with the experiment result.

Key words: helium atom, parameter perturbation method, ground state energy