Abstract: TiB2 coating was electrodeposited on graphite substrate from K2TiF6-KBF4-KF-KCl-LiF molten salts at 820°C for 3 hr with a current density 0.7 A/cm², of which the composition of the electrolyte used is 15 K2TiF6, 24 KBF4, 48KF, 8KCl, 5LiF in wt%. The penetration of sodium and electrolyte into the TiB2 coating used as cathode of aluminum electrolysis was studied. After electrolysis for 4 hr, the SEM analysis showed that Na, F and Al penetrated slightly into the TiB2 coating, and XRD pattern showed that there is a little NaF in the graphite substrate. Compared with graphite cathode, TiB2 coating can slow up. sodium formation and decelerate sodium penetration, but can not hinder sodium from penetration thoroughly.