Based on the capacity/demand (C/D) analysis of bridge components, and life cycle and performance based seismic design principles, a practical approach is developed for the seismic performance evaluation of superlong span cablestayed bridges. According to the approach, the seismic performance evaluation of the Sutong Bridge，which is a cablestayed bridge with a main span of 1 088 m, is completed, and the practicality of the approach is validated. The earthquake resistance level for superlong span cablestayed bridges is discussed, including the earthquake level, its corresponding structural performance and check indices. And a set of formula for capacity/demand ratio calculation of bridge components is proposed.