The invention discloses a three-core cable fusion joint, and relates to the technical field of electric power transmission. The joint comprises two mutually connected cables, an inner repairing layergroup and an outer repairing layer group, wherein the inner repairing layer group and the outer repairing layer group are used for repairing the cables, each cable includes three conductor cores and an outer protection layer group coated outside the three conductor cores, the outer protection layer group includes an inner sheath layer, an armor layer and an outer sheath layer in sequence, the outer repairing layer group includes an inner sheath repairing layer, an armor repairing layer and an outer sheath repairing layer in sequence, the outer sheath repairing layer is set to be a heat shrinkable casing, and two ends, which are lapped with the outer sheath repairing layer, of the outer sheath layer are sleeved with cold shrinkage casings. The cold shrinkable casings are great in elastic shrinkage force and can carry out permanent elastic coating on the lapping parts at two ends of the outer sheath repairing layer, thereby forming interference fit for a long time, and effectively improving the relative stability between two ends of the outer sheath repairing layer and the outer sheath layer. In addition, the cold shrinkable casings can firmly adhered to the outer side of the outer sheath layer, thereby effectively improving the waterproof performance of the cable after the repair.