By the principles of TIG and plasma welding, cast aluminum alloy piston for automobile are remelted with three methods respectively,which are traditional TIG,high frequency variable polarity TIG（VPTIG）and plasma. The depth of refining layer,the hardness of refining zone and primary silicon size are measured and analyzed. The result shows that the fine primary silicon size of 4.22 μm and high hardness of 182.4 HV can be acquired in the traditional TIG remelting method; The refining zone depth of 6.10 mm can be got by plasma remelting method,which is the deepest in these three methods; the treatment effect obtained by VPTIG remelting method is between the effects got by above two methods.