Abstract: The expressions of current intensity and Joule heat soure power due to the concendation effect are given at the moment while the crack is being formed in a current-carrying infinite plate . Based on the solution of heat conduction equation, the temperature field around the crack tips can be obtained It is shown in the examples that a small welded joint can be formed in a small sphere near the tip of the crack as the result of heat cocentration effect, at the transient moment when the time electromagnetic is applied So the propogation of the crack could be prevented .