The urban green belts mechanism was part of the city planning landscape of the 20th century for sustainable urban management. Greenbelt is a land-use policy and designation used in land use/land cover planning. The green belt has long been a design policy that also has a base in London accepted by other renowned cities such as Ottawa, Birmingham, Seoul, Frankfurt, Tehran's, Mashhad, Beijing, Gulbarga, Ontario, etc. Benefits include the value of living close to the green belts, recreational resources, productive farmland, transport connectivity, and a wide range of life support ecosystem services. The study investigated the present green space condition and its infrastructure with other cities around the world and prescribed the other mechanism in reviewing the Master Plan and the Detailed Area Plan of Chittagong city, Bangladesh along with a significant number of journal articles, books, and reports. The study found that the city of Chittagong is facing various problems in the present decades with its various problems like green space, recreational facilities, disaster, public health risk and so many. It also found that the city's geographical condition is suitable for developing an effective green belt in its periphery area. Although green wedges is another park system proposal for the barriers of urban green belt. The importance of land allocation for urban green space is usually neglected or easily reported in the city transition region. Besides, the city of Glasgow, Stockholm, Melbourne, and Copenhagen, etc. are accepted green wedges mechanisms. For some barriers as like as industrial development and some exclusive economic zone, some green wedges are much suitable in the gap of urban green belt in Chittagong city. The concept of green belt and green wedges both supports sustainable urban management in the city of Chittagong. However, these findings and analysis will be of great importance to the urban planners and decision-makers, for making environment-friendly sustainable future planning of modern and the planned Chittagong city.