A self-adaptive solution for the excessive axial force on the blades of a guide vane type turbine under high flow velocity conditions is proposed. This device maintains a relatively stable speed ratio in the low flow velocity range and reduces blade load by adjusting the speed ratio in the high flow velocity range, thereby improving the power output of the turbine in low flow velocity environments. Numerical analysis is conducted to investigate the adjustment range of the expansion angle, the length and shape of the movable device, the aspect ratio of the long and short axes, the thrust on the turbine and the power output under different flow velocity conditions. The research findings indicate that using an airfoil-shaped movable device with an aspect ratio of 1.5 and an expansion angle adjustment range of 0° to 15° can achieve a speed ratio adjustment range of 1.10 to 1.57. When the aspect ratio of the movable device is 3.4∶1, the relative force on the blades can be reduced to approximately 1.1 in the high flow velocity range, while maintaining good energy conversion efficiency in the low flow velocity range.