In order to reduce the tension of mooring system in shallow water, a constant tension mooring system suitable for floating wind turbines in shallow water is proposed. By increasing the height of the weight clump, the kinetic energy of the floating wind turbine is converted into the gravitational potential energy of the weight clump, ensuring that the maximal instantaneous tension of the mooring system is maintained at a low level and does not exceed the breaking tension of the mooring line. The wind, wave and current environmental conditions in the deep sea area of Zhejiang are adopted, and the depth of the target sea area is 60 m. Based on the frequency-domain potential flow theory and time-domain dynamic mooring analysis method, the coupling dynamic response of the floating wind turbine and constant tension mooring system of the WD225-9000 wind turbine is studied, and the effects of weight clump size and mooring line parameters are analyzed. Compared with the traditional catenary chain mooring system, the length and weight of the mooring line and the steel consumption of the anchor piles can be effectively reduced by the new constant tension mooring system. The constant tension mooring system maintains a constant tension due to the recovery force stiffness curve, which ensures the safety of the floating wind turbine mooring system in typhoons by preventing excessive mooring tension when the floating wind turbine experiences significant horizontal deviation under survival sea conditions. The proposed constant tension mooring system can also be applied to the tension leg floating wind turbines.