A mechanical arm having a shell and a lift power unit. A holding chamber is arranged in the mechanical arm shell, the lift power unit part is arranged in the holding chamber, the upper wall surface of the mechanical arm shell is provided with a first heat dissipation hole and a second heat dissipation hole. The first heat dissipation hole and the second heat dissipation hole are located on each side of the lift power unit, respectively. The lower wall surface of the mechanical arm shell is provided with a third heat dissipation hole and a fourth heat dissipation hole, and the third heat dissipation hole and the fourth heat dissipation hole are located on each side of the lift power unit, respectively.