In this paper, we carry out the theoretical calculation of line widths and energy shifts of spontaneous emission, the decaying oscillating field is taken instead of the free field as the action field. In the calculation the self consistent requirement is imposed.The method of calculation is rigorous but different from the previous workers. No divergence difficulties are encountered in the calculation.We think this method of avoiding divergence difficulties may be useful in the theoretical calculation of inelastic scattering cross sections in elementary particle physics.