The merit of elliptic orbit was analyzed, and the merit was that elliptic orbit could give a biasing of earth coverage towards a given latitudinal zone or a given region. The method of designing special elliptic orbit which was critical inclined, sun synchronous and repeating ground trace was expounded, and the calculation process of this method was summarized. The approach to design critical inclined, sun synchronous, repeating ground trace orbit constellation was proposed, and the time each satellite-s ground track passed the destination was taken as the key parameter to influence constellation performance. The mathematical models used in genetic algorithm(GA) for constellation optimization were introduced, and the parameters of constellation were optimized by GA. The statistic rule of optimization results was discussed, and the constellation which accorded with this rule was the constellation studied. The analysis result of constellation performance shows that this kind of constellation is fit for regional coverage.