Taking the 160 mm × 160 mm continuous casting billet as the research object, the numerical simulation was used to analyze the stress-strain distribution in the corner area of continuous casting billets with different fillets during rough rolling process. The internal and surface quality of different rounded continuous casting billets and the proportion of rolling wire cracks were studied through process experiments. The results indicate that as the fillet radius of cast billet increases, the equivalent strain and stress in the corner area decrease. In the process experiment, the surface vibration marks of continuous cast billet with the fillet radius of 8 mm were deep, and there were multiple fine strip-shaped pro-eutectoid ferrite  in the microstructure. The proportion of cracks in the rolled large-sized wire rod was high.The depth of surface vibration marks of continuous casting billet with fillet radius of 15 and 20 mm is reduced, and the microstructure is composed of blocky ferrite and a small amount of pearlite. The proportion of cracks in rolled large-sized wire rods is low. The friction force between crystallizer with the fillet radius of 20 mm and the corner of continuous casting billet increases, which can easily lead to production accidents such as steel leakage and breakage. The fillet radius of the 160 mm × 160 mm continuous casting billet crystallizer should be 15 mm.