The invention provides a robot and an arm structure thereof. The arm structure of the robot comprises a support arm, a wrist, a first driving motor, a second driving motor and an elbow joint, wherein the wrist is rotationally arranged on a first end of the support arm; the first driving motor is used for driving the support arm to rotate around the axis; the second driving motor is used for driving the wrist to rotate; the elbow joint is arranged on a second end of the support arm; the first driving motor and the second driving motor are respectively arranged in a joint casing of the elbow joint. The arm structure of the robot solves the problem of dispersed arrangement of the driving motors of the spraying robot in the prior art.