The invention discloses a robot arm part, which comprises a supporting arm, a first shaft rotationally connected with the supporting arm, a second shaft rotationally connected with the first shaft, first and second driving pieces arranged on the supporting arm, first and second bevel gears rotationally sleeved at two ends of the first shaft, a third bevel gear fixedly connected with the second shaft and meshed with the first and second bevel gears, a first transmission mechanism for transmitting the power of the first driving piece to the first bevel gear, and a second transmission mechanism for transmitting the power of the second driving piece to the second bevel gear, wherein the first, second and third bevel gears and the first shaft jointly form a differential gear train. The first transmission mechanism includes a first worm, a first worm gear, a first driving wheel, a first driven wheel and a first flexibility part coupled to the driving piece, and a first belt transmission mechanism connected between the first driven wheel and the first bevel gear. The robot arm part has the advantages of compact structure, and higher load bearing capacity.