When a suitable pulse current is introduced into a metal die containing a crack, the current concentration effect is immediately apparent, small welded joints are formed at a small sphere near the crack tip inside the metal die by metal melting as a result of the heat concentration effect. An axial symmetric metal die with a half–embedded crack on the top face is the object studied. The high intensity pulse current is switched on and flows from the outer to the inner surface of the hollow metal die. The complex function method is used to solve for the temperature field around the crack tip at the moment when the pulse current is switched on. The expression for the temperature field provides the basis for determining the current density and current direction. The experiment surveys show that the temperature around the crack tip grows up instantly above the melting point of the metal, the round crack tip is melted.