The invention discloses a mechanical arm structure for cultural relic repair. The mechanical arm structure comprises an adjusting mechanism and a repairing arm, the repairing arm is mounted on the adjusting mechanism, and the adjusting mechanism is used for adjusting the position of the repairing arm in the space; the repairing arm comprises an inner connecting disc, an upper inner shaft, a lowerinner shaft, a repairing cutter, an upper outer cylinder, a lower outer cylinder and a plurality of guiding ropes; and a first bearing and a second bearing are mounted on the inner connecting disc, the repairing cutter is detachably mounted on the lower part of the lower inner shaft, the upper outer cylinder is rotatably mounted on the upper inner shaft, the lower outer cylinder is rotatably mounted on the lower inner shaft, a second upper connecting frame is mounted on the lower part of the upper outer cylinder, a third bearing is mounted on the outer side of the second upper connecting frame, a fourth bearing is mounted on the outer side of the lower outer cylinder, guiding holes for allowing the guiding ropes to penetrate are formed in the outer circle of the third bearing, and the guiding ropes penetrate through the guiding holes and are connected with the outer circle of the fourth bearing. The mechanical arm structure is easy to manufacture and use, position change of the repairing cutter can be flexibly completed, and the problem of inconvenient operation by the human hand in the narrow space is effectively solved.