Abstract: According to transverse corner cracks occurred on 200 mm casting slab of V or V-Nb microalloying low carbon auto frame steels produced at Pangang Steel, with coniprehensive-optimized casting process parameters including decreasing the ratio heat flux between nan'ow side and broad side of slab in mold from original 0. 90 ~ 1. 10 to 0. 75 ~ 0. 85, decreasing the mold powder viscosity from 0. 20 Pa • s to 0. 16 Pa • s, stabilizing the casting speed and working condition of caster, the casting slab transverse corner crack defects significantly reduce and the hot rolled coil lines and peeling defects caused by the transverse corner cracks of slab are eliminated, therefore the percentage of changing criterion or reducing to lower grade caused by surface defects of auto frame steel hot rolled coil decreases to 0 from original 30%.