Stark modulation electric rotation laser spectroscopy (SM ERS) was used to separate the electric rotation signal produced by the accidental degenerate transitions from the nondegenerate transitions. It can simplify complex and congested electric spectra and is very valuable for measuring perturbed polyatomic molecular spectrum. In this paper the semi classical theoretical model of this technique is presented. As an example, the NO 2 SM ERS spectrum and their main character was analysed by perturbation theory.