Abstract: The leaking of nozzle stub of boiler furnace at service was discovered and investigated.The results show that the temperature at welding joint is too high and lead grain become bulky in heat-affected zone.Some restraint stress and cracks are produced in welding joint for the fast cooling velocity after welding at heat-affected zone in steel 102,subscale is formed at repairing welding and lead the existence crack extended further,nozzle stub leaked at crack finally.