The invention provides a preparation method of WC-Co series nano-composite hard alloy powder, which includes: installing the front cover plate and electrode rod of the ball mill tank, and connecting the front cover plate and electrode rod to the two poles of the plasma power supply respectively ; Put grinding balls and a certain proportion of W, C, Co raw materials in the ball milling tank, and when the electrode rod contacts the grinding balls and W, C, Co raw materials, cover the rear cover of the ball milling tank; pass the vacuum valve Vacuum the closed ball mill tank to 0.01-0.1Pa, or pass the discharge gas medium through the vacuum valve until the pressure is 0.01-0.1MPa; turn on the plasma power supply, according to the discharge gas medium and its pressure Adjust the discharge parameters and carry out different types of corona discharge plasma high-energy ball milling; take out the mixed powder of W, C, and Co, place it in a heat source environment for synthesis reaction, and obtain the corresponding cemented carbide. The invention can not only save energy, but also improve synthesis efficiency.