Three-cable position system is one of crucial position equipments effecting capacity and safety for cutter suction dredger. Aiming at design of three-cable positioning system，this paper introduces the main components，working principle and design process，forms the calculation process of the external loads borne by the three cable system under different working conditions，analyzes the variation law of the cable tension and the stress characteristics of the cylinder structure by using the methods of frequency domain analysis and finite element analysis，and proposes cable type selection and local structural design method. The results show that under various working conditions，the cable tension increases with the increase of wind speed，and under the same wind and wave conditions，the cable tensions under dredging operation conditions and wind shelter conditions are different quitely，which should be comprehensively considered. In addition，in the design process of three-cable positioning system，special consideration and key strengthening should be given to the parts with large stress.