Abstract: With the high-speed development of national economy,China’s urbanization has taken a fast-progessing track.In some relatively highly developed areas,dramatic changes have taken place in the spacial structure of big cities.The most notable characteristic is the transition from the simple form of a single city to a most complicated structure of metropolis,which is based on the core city surrounding by numerous cities and regions.The four metropolitan areas such as SH,BJ,GZ and SY have formed the preliminary shape,meanwhile,in the surrounding areas of those big and medium-sized cities with relatively high development economy and society,some regional metropolises and local metropolises are taking shapes as well.The formation and development of these metropolises has a very important supporting role to the social development of our regional economy.There is a consensus in adopting the metropolitan development strategy with an unbalanced growing pattern so as to promote the social development of our regional economy.However,the buildup of metropolises is confronted with many problems in the area of environment,land resources,transportation,energy and industries.Transportation is the most prominent issue among all these problems.The construction of a modern transportation system in the metropolis is most significant in terms of enhancing the connection of core city and surrounding towns and areas,helping the integration of land use in cities within the metropolis,boosting the joint construction and use of cross-region infrastructure;protecting and utilizing all kinds of resources,improving the living and investing environment and realizing the integration of metropolis.But the construction of the transportation system in the metropolis development strategy is sometimes accompanied by blindness.This article starts with analysis of the spacial structure and transportation requirements in the metropolis and discusses about the role and function of light rail transit with medium freight volume in public transportation.Taking into account of the issues in the development of light rail public transportation,the author makes a point that the development of public transportation with light rail transit with medium freight volume as the backbone is an important approach in the metropolis,provides many suggestions for the planning of comprehensive transportation system based on the light rail transit with medium freight volume in a metropolis.