The assessment index system of a smart grid is the carrier that scientifically assesses the development level and effectiveness of the smart grid and the foundation of smart grid construction. The index system of smart grid is divided into the strategic index set and process index set. As the former represents the macroscopic features while the latter represents the microscopic factors of the smart grid， they are connected by an index chain. The strategic index set is constructed by quantifying the demands based on the multilevel demand architecture of the smart grid stakeholders. The process index set is established by multidimensional decomposition and transformation of the strategic indices. The index system proposed is highly hierarchical， distinctly associated， and convenient to use.