Abstract: The yttrium is selected as the refiner for ZL101 alloy, meanwhile the electromagnetic stirring device, which is controlled by changing the frequency of electric current, is used to stir the ZL101 alloy for a few seconds. Mechanism of using rare earth to refine the semi-solid alloy and effects of different frequencies on microstructure of primary α phase in different areas of the cast ingot as well as the best parameter of the electromagnetic stirring frequency are discussed. The results indicate that the liquid ZL101 alloy that poured at low superheat temperature (620 ℃) is slightly electromagnetic-stirred under the condition of 30 Hz and 15 s for a short time and then holding at 590 ℃ for 5 min, the morphology and grain size of primary α phase reach the optimal state. The average equal-area circle diameter of grain in the core area is 64.95 μm and the average shape factor is 0.80; while the average equal-area circle diameter of grain in the edge area is 58.98 μm and the average shape factor is 0.83. Under this condition, the morphology and grain size of primary α phase in semisolid ZL101 alloy slurry are quite satisfactory but more uniformly distributed along the radial direction.