At the beginning of the commissioning of slab casters at Chongqing Iron and Steel Co., Ltd., the ratio of the slabs without surface defects was very low. The main surface defects are longitudinal cracks, transverse corner cracks and longitudinal off-corner depression and so on. In addition, the smooth of CC process and the slab surface quality were influenced by the sticky in the mould. The control measures were introduced following the analysis and investigation for the cause of the defects. The ratio of the slab without surface defects was increased to more than 90% and the basic condition for the hot charging of slabs is achieved.