Based on the concept of ecosystem services and welfare, a definition of a sustainable city is proposed, and a quantitative model to describe sustainable welfare is established. With the analysis of the major issues and driving forces of sustainable city construction in China, the approaches for sustainable city construction are proposed as follows: to promote study on the theory and methodology of sustainable city construction, to set up and perfect institutional and management systems, and to establish a performance assessment system and an effective operation mechanism for sustainable city construction in China.