Abstract: A357 aluminum alloy billets were continuously rheocast by annular electromagnetic stirring (A-EMS),and the effects of stirring current,stirring frequency and annular gap width on billet microstructures were analyzed.It is shown that more uniform microstructures of A357 aluminum alloy billets from the edge to center can be produced by A-EMS,and the primary α(Al) phase is spherical or rosette-like.With the stirring current or the stirring frequency increasing,the rosette-like primary α(Al) phase decreases significantly on the billet microstructures,and the nondendritic primary α(Al) is finer and more spherical.Narrow annular gap is advantageous to obtain uniformly fine spherical solidification structures.