Numerical calculation and mercury model experiment are performed to analyze jet flow under DC magnetic field and it is found that counter flow generated around the jet flow. Both the results of calculation and theoretical analysis show that the distribution of electric current density is an important factor for generating counter flow. It is also predicted from numerical calculation that the counter flow has a great effect on the molten steel flow in the mold, therefore there is a possibility for the counter flow to have a great effect on slab quality.