The ship lock capacity is one of the most important factors to determine the size of ship lock.The sea ship lock in fishing port is almost under the complicated hydrologic condition,and it becomes extremely important to calculate the capacity reasonably.Based on the water depth for ships’safety navigation and the characteristics of hydrologic condition,we establish the actual tidal time calculating model under cumulative frequency of certain high tide level,and divide the capacity into flat tide period and tide period.Considering time that ship move in the lock,we revise the calculating method of traffic capacity in tide period,and introduce the concept of unit ships.The concept can simplify the selection and combination of ship types,and the determination the number of ships in one lockage is more convenient and accurate.The calculation of traffic capacity in flat tide period is based on the water depth and the tide waves under special organization model.The influences of organization form of ship lock operation and the service level also should be considered to make the result more reasonable.