At present，there are four lanes of locks in Changzhou multi-purpose dam.The down bound cargo volume in 2021 reached 119 million tons and was close to the capacity of locks.In the study of scheme for a new lock，the capacity of existing locks and the new lock should be analyzed in accordance with the cargo volume forecast.The formation of vessels through the lock and the average dead weight tonnage and loading rate of each class of vessels are predicted.Based on discrete event system simulation，a model of lock group is built，simulating the random arrival of vessels and ship arrangement algorithm in lock chamber，and considering different ship distribution rules among multi-lane locks.The results show that the total capacity of lock group is relatively optimal if ship enters lock by its arriving order.Besides，the fifth lock should be built at a new location and plane dimension of 340 m ×34 m is suitable for it.