Abstract: Abstract: cast steel memorial archway is the key component of wide and heavy plate finishing mill, which has large weight, large volume, large cross-sectional area and large rigidity, and the crack is easy to expand after crack. at present, the cracks are basically repaired by milling and removing cracks. this way will lead to the reduction of the cross-sectional area of the archway and the rolling force, which can not meet the requirements of normal use and affect production. According to the material and crack characteristics of the archway, combined with the bearing capacity of the production site, this paper analyzes the causes of the cracking of the archway and the weldability of the cast steel archway, formulates the on-line repair process, and carries on the on-line welding repair to the archway of the finishing mill. the repaired archway meets the normal use requirements, ensures the rolling quality of the wide and heavy plate finishing mill, prolongs the service life of the equipment, and saves a lot of money and time.