As an important energy consuming channel， electric power plays a considerable role in reducing fossil energy consumption and cutting down CO2emissions. The significance of developing low-carbon electricity is illustrated， and the necessity for establishing a smart grid's index system is pointed out. The functions of the smart grid's low-carbon index system are discussed. The aim and outcome of the system are defined. The relative design principle， method and evaluation indices as well as the realization steps are presented. A look ahead is given to the application of the index system.