An evaluation algorithm of the pupil characteristic parameters is proposed, aiming at the practical application requirements of lithography illumination system. By changing the intensity distribution of pupil, this algorithm can be used to simultaneously calculate the pupil ellipticity, non-balance_X, non-balance_Y, non-balance_quad, and other pupil characteristic parameters in different illumination modes. The relay lens set of the 28 nm node scanning lithography illumination system is used as an example and the pupil characteristic parameters under the traditional illumination mode are analyzed. The simulation results show that the maximum value of pupil ellipticity in the full field of view is 0.95%, and the maximum values of non-balance_X and non-balance_Y are 0.18% and 0.19%, respectively. In addition, the maximum value of non-balance_quad is 0.66%. These data satisfy the actual index requirements of the 28 nm node scanning lithography. The proposed algorithm can help to evaluate the pupil performances quickly at the optical design stage.