Abstract: The math modeling of distribution of flux flow field and analysis on pressure of meniscus in mold have been carried out by commercial software Fluent. The flow rate of flux was maximum at time t =0 during a oscillation circle,at that time the minus pressure on solidified shell was produced by flux, therefore it should be to decrease the minus pressure in time as far as possible,in order to decrease frictional force for flux easy flowing in.The modeling results conform to the real condition of billet concasting at Nanjing Steel.