The invention discloses a four-upright semi-submersible type
floating wind turbine foundation with a
ballast. The four-upright semi-submersible type
floating wind turbine foundation comprises four uprights, wherein three uprights are side uprights, and the other one is the middle upright. The three side uprights are arrayed at equal intervals to define an equilateral triangle. Each side upright isequipped with a square cabin, and the three side uprights are vertically arranged on the corresponding square cabins. The middle upright is located at the
centroid of the equilateral triangle and isequipped with a circular cabin, and the middle upright is arranged on the circular cabin. Each square cabin and the circular cabin are connected through a variable cross-section rectangular
buoy. A transition platform is arranged at the connecting position of the top of the middle upright and a
tower tube of a wind
turbine, an inclined strut is adopted between the tradition platform and each variable cross-section rectangular
buoy to transmit the
bending moment load of the whole wind
turbine, and connecting bridges are arranged between the inclined struts and the variable cross-section rectangular buoys. The four-upright semi-submersible type
floating wind turbine foundation with the
ballast provides a safe, reliable and cost-controllable offshore supporting structure for large megawatt wind
turbine unit (above 7MW), and guarantees stable, safe and reliable operation of the large megawatt wind turbine unit.