In order to improve the mould filling ability, the method for production of thin-walled castings in the travelingmagnetic field was applied. The relationship between magnetic field density and input voltage as well as distancewas investigated, and the mould filling length of A357 melt has been studied. The electromagnetic forcesappliedon the melt were also analyzed. The result shows that the mould-filling length of the melt increase rapidly with theincrease of magnetic flux density. The mould filling lengths in gypsum upper mould and magnetic material uppermould were compared from the standpoint of application. It demonstrated that the steel upper mould is superior togypsum mould.