A robot arm assembly includes a plurality of driving members, a first transmission mechanism, a second transmission mechanism, and a third transmission mechanism. The first transmission mechanism includes a first rotating shaft, and a second rotating shaft. One end of the first rotating shaft is connected to the first driving member by the connecting member, the other end of the first rotating shaft is movably connected to the second rotating shaft, and the first driving member drives the first rotating shaft to rotate a predetermined number of degrees. The second and third transmission mechanisms include several connecting members and jointing members, transmission members and shafts, and gear wheels.