Abstract: When producing peritectic steel slabs with an aspect ratio (width-thickness ratio) greater than 10 by continuous casting, the incidence of longitudinal surface cracks in continuous casting slabs is significantly higher than that of conventional slabs, which has become a core problem restricting product quality. Key process control points, including mold cooling water flow rate, mold cooling water temperature, mold taper, mold flux, and submerged entry nozzle (SEN) type, were emphatically analyzed and studied, and targeted process improvement measures were adopted. The practical results show that by controlling the inlet temperature of mold cooling water at 33-38 ℃, the water gap flow rate of the wide-side copper plate of the mold at 6.23 m/s, and the mold taper at 1.10%-1.15%, as well as adopting high-basicity mold flux and convex-bottom SEN, the incidence of longitudinal surface cracks in peritectic steel slabs with high aspect ratio is reduced from 13% to 0.38%, and the longitudinal surface cracks of the slabs are effectively controlled.