Buffer rod is an important part for connecting buffer system of locomotive and rolling stock. Its material is generally 45 steel. Under suitable welding current,welding voltage,welding speed and wire feed rate,the structure,hardness,tensile property,impact property and metallographic structure of surfacing layer and HAZ of 45 steel by cold metal transition were studied. The results show that the mechanical property of the surfacing repair zone improves obviously comparing with that of buffer rod 45 steel base metal when the current is 150～160 A,voltage is 15～16 V,wire feed rate is 5 m/min,welding speed is 12 mm/s and the mixed gas flow is 20～25 L/min. The repaired buffer rod has no welding defects after magnetic powder and ultrasonic flaw detection. The repair process improves the service life of the buffer rod.