Abstract: For the higher incidence of transverse corner cracks of CCSA slab in a steelmaking plant,it is analyzed that the main reason of transverse corner cracks is unreasonable temperature distribution caused by secondary cooling system,based on the research of high temperature mechanical property of CSSA and the measurement of slab surface temperature.So two measures have been taken to optimize the secondary cooling system:firstly,part of the nozzle types is changed and the nozzle arrangement was adjusted;secondly,secondary cooling water is optimized by the modified solidification heat transfer model of slab continuous casting.The industrial test shows that the temperature at the corner of slab is improved and the rate of transverse corner crack is reduced from 3.7% to 0.41% after optimization.