Nanostructured bulk of W-Cu alloy was prepared by mechanical alloying and hot pressed sintering. The nanostructured W-Cu material shows the characteristic of the spreading electric arcs, and the commercially used W-Cu alloy exhibits the characteristic of the localized arcs during the electric breakdown. The effect of nanostructured W-Cu alloy is caused by a larger number of electrons emitted during the discharge with a low electron work function, and highly conductive grain boundaries and many nano-metre-scale grains could narrow the potential barrier at the tungsten-copper interface.