The existing models of population distribution often focus on the region with a single city or even multiple centers, and lack the detailed explorations of the common and special type of urbanization areas with two centers. Taking Beijing-Tianjin region of China, which is a distinct dual-nuclei metropolitan area in the world, as an example and choosing Landsat-5 TM image in 2005, population, etc. As the data, this paper devotes to comprehending and illus-trating a model of Cassini growth of population between the two metropolitan cities through the research of spatial population distribution pattern, aided with RS and GIS techniques. Main technical processes include Kriging interpola-tion of the population data and character simulation of the Cassini ovals. According to the calculation of a/b, a key characteristic index of Cassini growth model, the spatial structures of population distribution were given. When a/b1,it is a curve with two separated loops with a population density more than 3000 persons/km2. When a/b=1, it is a lem-niscate curve with a population density about 3000 persons/km2. When 1