Abstract: asting nozzle is the decisive factor affecting the fluid field of the magnesium alloy. The uniformity of the fluid velocity distribution directly affects slab quality. This paper performs the numerical simulation on the flow field of the magnesium alloy in different casting nozzle structures using AZ31 magnesium alloy horizontal twin-roll continuous casting nozzle structure with the width of 1 500 mm. The effects of nozzle length, sidewall shape, wake region length on the fluid velocity distribution uniformity at the outlet of casting nozzle are analyzed. The results show that the nozzle length and wake region length positive correlate to the fluid velocity distribution uniformity. Casting nozzle with diverging sidewall leads to uniform fluid velocity distribution.