Upper arm of robot

The invention discloses an upper arm of a robot. The upper arm comprises a wrist joint power input device and a wrist joint. The wrist joint power input device comprises a fourth joint servo motor, a fifth joint servo motor, a sixth joint servo motor, and a motor protection cover. The wrist joint comprises a fourth joint reducer, a fifth joint reducer, a sixth joint reducer, a fourth joint power shaft, a fifth joint power shaft, a sixth joint power shaft, a fourth joint rotation arm, a fifth joint rotation arm and a tail-end mechanical flange. The fifth joint power shaft is arranged in the sixth joint power shaft, and the sixth joint power shaft is arranged in the fourth joint power shaft. The upper arm of the robot is compact in structure, easy to assemble, high in transmission efficiency, adjustable in gear clearance, small in overall volume of wrists of the industrial robot, flexible and portable; the fifth and sixth joints are same in modulus optimization, part specifications can be reduced, butch production can be facilitated, and the problems about dispersion of power distribution and routing of servo motor cables in an original structure can be solved.