The different method used to calculate the energy level of the Dirac equation and limit the energy level between 0<E<1, but the NU method here calculated the first time for the Dirac spinor equation. The result calculated by us has validity with others researcher who calculated using power series, hypergeometric method, and other mathematical methods. The validity is check for both low and high atomic masses has a good agreement. The energy equation calculated depend upon quantum numbers, central potential, and Fine structure. The developed equation (9) when studies with atomic number show energy level decrease with increases atomic number and increase with an azimuthal quantum number. The developed equation (9) is similar to Nendzing, Ekeren and Bethe et al. calculated for relativistic cases using different method rather than the NU method.