Dredging works are huge in water transportation engineering construction projects，and the investment accounts for a large proportion. To control the project investment，the dredging ship type should be selected reasonably according to the situation of the project. Based on the current dredging quota，this paper analyzes the price composition and influencing factors，constructs the relationship curves between the comprehensive unit prices of the dredging projects and volumes at the same haul distance when the ship type and specification change，summarizes the economical and applicable dredging volume ranges of different ship types，and analyzes the change trend of unit prices. Then this paper constructs comprehensive unit prices and transportation distances curve diagrams，and finds the balance point of the quantity and economical haul distance. The results show that when the volume is large enough，we prefer large-scale ships；and when the distance is long enough，we prefer grab dredgers and self-propelled mud barges to self-propelled trailing suction dredgers.