Abstract: Moisture migration in medium voltage cable joints can easily lead to insulation deterioration, which can cause power outages in serious cases.Therefore, it is of great engineering value to study the moisture diffusion path of cable joints and find out which parts of the joints are likely to cause moisture intrusion.The water diffusion law in the actual joint was studied through accelerated damping experiments of different joint samples, including water intrusion site and diffusion path.The results showed that water diffusion in the joint was a process of infiltration and in-depth layer by layer from the outside to the inside.Among them, the decline of the adhesion between waterproof tape and the inner and outer sheath of the cable and the existence of armored connecting wire were the key factors that caused the rapid diffusion of moisture outside the main body of the joint.Water diffusion at the composite interface of cross-linked ployethylene (XLPE) and silicone rubber (SiR) inside the main body of the joint was mainly axial diffusion.