It can provide effective evidence for expressway traffic control and construction planning by effectively identifying congestion of expressway. A methodology of congestion discrimination was proposed based on travel time threshold. The travel time collections of all vehicles were extracted based on toll gantry data. The travel time collection was clustered and analyzed by clustering algorithm, and the travel time threshold of different congestion levels was calibrated according to the clustering results. The congestion condition will be discriminated based on the congestion travel time thresholds. The results indicates that the overall operation of Guangzhou expressways is good, with 80% of periods and sections being in a smooth state.