Abstract: In this paper we have carried out theoretical calculation on the energy levels of ruby by means of theoretical methods of the field theory^[1]. In the calculations we have considered all electrostatic interactions, octahedral-field potential and trigonal-field potential and spin-orbital coupling interaction of the d3 configuration. The calculated energy levels and splittings coincide better with experimental values. In this paper we have also discussed effects of various parameters on energy levels and splittings.