The application for FC-Mold (Flow Control Mold) technology is researched in Ansteel slab caster, and the fluctuations of liquid steel in different parameters are emphasis researched. The results show that the fluctuation of liquid steel can be decreased 50% by using FC-Mold, and the value is decreased from ± 5mm to ± 2mm. The casting velocity can be increased by using FC-Mold. The effect of FC-Mold is increased with increasing of current. And FC-Mold can restrain the unstable liquid steel from velocity changing. The statistic application results for 610 strands show that the degraded ratio for automobile steel is decreased 6%.