Abstract: The Traffic Congestion Index（TCI） for ports is introduced and the modeling and calculation of the index is conducted based on AIS data. The experience on road traffic is used to develop the index system. In order to establish TCI, the VTS reporting line of the port is moved outwards to ensure the AIS reporting zone to cover all roadsteads. The time of every ship′s entering the port, staying at berth and leaving the port are respectively calculated according to AIS data. The ratio of actual in-port time of ships to in-port time reference is defined as the indicator of port congestion. The time ratio for each ship is weighted according to its cargo type and ship length. The weighted time ratios for ships are combined to get the TCI of the port. Tianjin Port, Shenzhen Port and Ningbo Zhoushan Port are examined with the TCI for illustration.