One of the important signs of the port. The conditions of the port and the basic boundaries for the use of ships are shown. Increasing the water depth can accept the larger ships, but will increase the amount of dredging and increase the cost and maintenance of the port hydraulic structure. Under the premise of ensuring the ship's driving and berthing safety, the water depth of the port can be determined separately according to the use requirements. For tidal harbour, when dredging volume of the entrance channel is too large, the ship shall be considered to be in and out of port. The port of modern port for large dry cargo ship dock water depth of 10 ~ 15 meters, large tanker terminal 10 ~ 20 meters.