Abstract: In view of the classification of damage states and quantification of damage index of bridge structures under earthquakes, based on the relationship between the damage states of bridge structures and their traffic capacity, this study classifies post-earthquake performance states into four levels for bridge structures and gives performance standard for each state. Based on the classification, this study selects 32 RC single reinforced concrete bridge piers and establishes their finite element models, Each RC single bridge pier model is firstly subjected to 80 near-field (NF) pulse-like ground motions. Subsequently, these models with different damages and residual lateral deformations are analyzed by pushdown analysis method after nonlinear time history analysis (NTHA), and the vertical bearing capacity curve of each model with different residual drift ratio is obtained. Then, based on the relationship between vertical bearing capacity of bridge piers and traffic capacity of bridge structures, the corresponding residual drift ratio thresholds for bridge structures under different function levels are determined by probability and statistics analysis. Finally, the seismic performance evaluation index system in terms of residual drift ratio is established for RC bridge piers, and the residual lateral drift ratios corresponding to the four performance states of post-earthquake bridge structures are respectively 0.07%, 0.33%, 0.65%, and 1.05%. The index system provides reference for further seismic performance analysis and post-earthquake function evaluation of bridge structures.