Newton's understanding of solar system opened a new era of human civilization. Accordingly, the understanding of galaxies will stimulate a new period of human social harmony. Galaxies are the most independent components of the universe. A massive Hubble Space Telescope photos survey reveals that the diversity of galaxies in the early universe was as varied as the many galaxy types seen today. In 2001, I proposed the rational model of galaxy structure. Now in this paper I present a preliminary rational structure theory. The mathematical background needed is no more than the preliminary results of traditional college courses of complex functions and partial differential equations. Its application to barred galaxies is discussed. If the application is successful then three simple and important examples of its testification are, the structural simulation of barred galaxy light distribution with rational structure, the simulation of spiral arms with the Darwin curves of rational structure, and the simulation of observational galaxy kinematics (e.g., rotation curves) with the New Universal Gravity dictated by the rational structure and the principle of force line conservation.