In the electroslag casting process, the melting droplets separate from the end of electrode and get to the cast region through slag pool. The volume and forming  time of the droplet are related with melting rate and material purification rate directly. In this paper, based on the temperature field, flow field and electric field,  acoupled mathematic model has been built. The fractional step method has been used to simulate the process that the droplet formed by gravity, slag buoyancy and interfacial tension between slag and melting metal. At the
 same time, the rule of droplet volume and forming time changing with different technology parameters has been studied. It is significant to improve electroslag casting technology being used widely.