PURPOSE: A backstrip welding method of a mold is provided to alloy the damaged part of the mold by repeating a process of generating a melting part by rapidly radiating low heat input of laser beam in a given pattern of radiating at a high speed and rapidly cooling the melting part with cold air. CONSTITUTION: A backstrip welding method of a mold comprises next steps. Metal powder(30) is supplied to the damaged part(B) on the surface of the mold(10) to have a given height. Low heat input of laser beam(LB) is radiated to the damaged part of the metal-powder supplied mold in a given pattern of radiating at a given welding speed. A part of the damaged part of the mold along with the metal powder generates a melting part(40). Cold air is supplied to the melting part through an air nozzle to rapidly cool the melting part. The laser beam consists of Nd:YAG laser beam oscillated from an Nd:YAG laser oscillator. The output of the laser beam is within in a range of 3.2~3.8Kw.
