There are 3 large vertical-arc slab casters in Chongqing iron and steel. The 3 slab castera are used to cast low carbon low silicon steel which is bulge easily and crack sensitive peritectic steel. Since production from the end of 2009， several productions had been occurred such as clamping of steel in the corner of the mold and bulging in narrow face of the mold. A series of improvements were conducted in 2009. Since 2013， the mold functioned well and the amount of production gradually decreased. In 2017， the amount of production increased， the mold assembly quality could not meet the production requirements， and re-examination of the mold repair and monitoring technology is becoming necessary.