The invention discloses a cross-brace device for a large vertical axis wind turbine, and belongs to the field of wind power generation. The cross-brace device comprises a fixed cross-brace, a movablecross-brace, a connecting shaft and a driving mechanism; and the fixed cross-brace is connected with the movable cross-brace through the connecting shaft. The cross-brace device has the functions of connecting blades, improving self-starting performance and reducing rotating speed. The movable cross-brace is arranged on the cross-brace structure, the air resistance is changed by changing the windward area of a cross-brace, and then a starting moment of a vertical axis fan is increased under the static state of low wind speed while the rotating speed is reduced under the condition of high windspeed, so that the functions of improving self-starting performance and adjusting the rotating speed of the wind turbine are achieved; and the cross-brace device can solve the problems of inherent poor aerodynamic performance and rotating speed control of the vertical axis fan, and can reduce the impact of additional equipment on the overall structure and aerodynamic performance of the vertical axis fan to the greatest extent at the same time.