The invention discloses a mechanical arm for local discharge detection of a switch cabinet and a control method. A lifting joint, a slide joint, a shoulder rotating joint, an elbow rotating joint and a wrist rotating joint connected in sequence are used; the wrist rotating joint is connected with a local discharge detecting sensor through a flexible connecting mechanism; the slide joint and the lifting joint are arranged in an axis perpendicularity manner, and respectively drive the local discharge detecting sensor to relatively move in the vertical and horizontal directions of the switch cabinet; and through rotating cooperation of the shoulder rotating joint, the elbow rotating joint and the wrist rotating joint, further adjustment of the position of a detecting point and the gesture of the local discharge detecting sensor is realized when relative positions of the local discharge detecting sensor and the switch cabinet are invariable, and precise detection is realized.