A wind turbine blade assembly includes a rotary shaft, and a plurality of blade units connected to the rotary shaft and angularly spaced apart from each other. Each blade unit includes a grid frame connected to the rotary shaft and formed with a plurality of grid spaces, a plurality of blade panels swingably connected to the grid frame and corresponding in position to the grid spaces, and a plurality of counterweight members respectively disposed on the swing ends of the blade panels. Each counterweight member includes a soft hollow main body and a counterweight fluid accommodated in the main body.