The contemporary new towns were a solution to the problems of suburban sprawl, demographic growth and the housing and employment shortage, congestion, land speculation, etc. But the environmental question perhaps related to the context of their creation (often after a period of crisis like war destruction), did not have priority in the decision-makings even if it were one of the fundamental pillars of the creation of the geneses of the new towns, i.e. the "garden-cities". The satellite model of town represents the concretization of the idea of the garden-city and then the new towns. It consists on a decentralization or polarization of the large cities and seeks to achieve several goals such as valorization of the suburbs, balance of employment-habitat, to relieve congestion the great centre and to stop the progressive extension of the large cities. The new news represents at the same time a new form of urbanization based on the principle of "table rase" (designing from zero) and the methods of expertise. Since 1970, the sustainable development makes its appearance and in particular the question of the environment is proposed for the cities and any urban project. Town and urban planning seek to integrate the principles of the sustainable development in the design or rehabilitation of cities. The multiplicity of the actors of the city and in particular the implication of the citizens, (in France promoted by law SRU) as well as the necessity to take into account of the environmental stakes imposes the development of tools for decisionmaking supports. These tools will have to be able to represent the consequences, in particular urban projects on the environment in order to control the dispersion of the opinions between the actors. At present a certain number of researches were undertaken in order to assess the durability of the projects of installation. An environmental approach to town planning (AEU) developed by French environment and energy management Agency (ADEME) undoubtedly constitutes the tool having the most retreat in terms of experiment. Nevertheless none of these tools clearly sticks to explain the relations between the urban form and the environmental impacts. Moreover many works aim to describe the urban form in term of mobility, accessibility or of density (Newman and Kenworthy, 1989; Frey, 1999; Newton, 2000; Williams et al., 2000). This thesis initially seeks to find out the convergences between the movement of the new towns and their geneses (garden cities) with the principles of sustainable development in particular with regard to environmental questions. The object of this work of thesis is to determine among the tools of environmental assessment the one or the ones that can be exploited in order to assess the relation between the urban form and the environmental impacts to answer the more general objective of decision-making support. We will propose an assessment method of the urban form and structure based on the method of network of Sorensen (1971) in order to know their role on the impacts caused on the environment. The work of this author was adapted to our research allowing the characterization interrelationships between the elements of the urban form and the environmental impacts. Finally the new town of Marne-la-Vallée is the subject of application of our method of environmental assessment