The microstructure of AlSi7Mg casting alloy is investigated by means of liquidus semi-continuous casting. Fine equiaxed non-dendrite grains of primary microstructure were obtained at liquidous.The average equal-area-circle grain diameter is 34.5μm,the minimum diameter is 5.8μm, the maximum diameter is 92μm.The average roundness is 1.88, the minimum roundness is 1.18, and the maximum roundness is 5.82.