The invention provides a robot and an arm structure thereof. The arm structure of the robot comprises a supporting arm, a wrist, a tail end arm, a first driving motor, a second driving motor, a third driving motor and an elbow joint, wherein the wrist is rotationally arranged at the first end of the supporting arm; the tail end arm is rotationally arranged on the wrist; the first driving motor is used for driving the supporting arm to rotate around the axis of the supporting arm; the second driving motor is used for driving the wrist to rotate; the third driving motor is used for driving the tail end arm to rotate; the elbow joint is arranged at the second end of the supporting arm; the first driving motor, the second driving motor and the third driving motor are all mounted in the casing of the elbow joint. The arm structure of the robot solves the problem in the prior art that all driving motors of a spraying robot are decentralized in distribution.