Abstract: Three different electrodes with different granularities medium carbon ferromanganese had been studied.The researches include welding technology performance of electrodes, the microstructure of deposited metal, chemical composition and impact toughness of deposited metal.The results showed that by adding nano medium carbon ferromanganese, the arc stability is better, the nano granule can increase nucleation core of crystal which play a role in grain refining, meanwhile the nano grain is burned badly, the deoxidation and desulfidation are weaken, impact toughness of deposited metal is reduced due to the overabundance oxide slag.