A robot arm assembly includes a first robot arm and a second robot arm; the second robot arm is rotatably connected to the first robot arm. The first robot arm includes a first sleeve, a first input shaft, and a second input shaft. The first input shaft and the second input shaft are seated in the first sleeve. The second robot arm includes a second sleeve and an output shaft; the output shaft is received in the second sleeve. The first input shaft is connected to the second sleeve via a pair of bevel gears, and drives the second sleeve to swing relative to the first sleeve. The second input shaft is connected to the output shaft via a plurality of bevel gears meshing with each other, and drives the output shaft to rotate relative to the second sleeve.