Population growth and rapid urbanization growth in recent decades have not only led to unbalanced physical expansion of cities, but also contributed to growth and development of cities. The city of Sari in Iran, like many other cities is not immune from these changes. The city population has increased by 16 times over the last fifty years. Therefore, the increasing population growth has created uncontrolled physical expansion in the city. In order to prevent these inefficiencies of urban problems, the present study was accomplished to determine the factors influencing the process of expanding the city of Sari and to find out some solutions to fix and prevent this process. The method used in this study, descriptive–analytical method, to data analysis and Heldern and Shannon entropy model were used. The results show that: 82% of the physical growth of the city during the period 1977-2005 was related to the population growth and the remaining 18 percent, was associated with the horizontal growth. The city sprawl, the metropolitan area of the city had denser structure and the surrounding areas had a more dispersed structure. Also the effects of synthetic and natural factors restricting the city of Sari physical development made the city exorbitance horizontal and linearly developed. According to the findings that could help prevent the horizontal development of the city, it could be said that we could make the city vertically developed rather than horizontal expansion, improvement and renovation of old texture of implementation and more use of the land, filling the empty spaces.