City is the origin of force to promoting low-carbon economy. This paper analyzes the restraint factors under the development of low-carbon city in China, establishes a dynamic system framework for low-carbon city based on economy, society, energy, environment, technology and urban construction. Then, the author illustrates the characteristics and necessity for the transformation from a old industrial base to a low-carbon city taken Chongqing as example, meanwhile, establishes the developing routes of low-carbon city in Chongqing.