Abstract: Studies the microstructure of the semi-solid slurry of ZL201 alloy in AC electromagnetic field where a stirring or oscillating action is exerting on the alloy melt. The results show that the AC electromagnetic field has an obvious refining effect on the microstructure of the alloy slurry, i.e. the fine near-spherical crystal grains take place in the vicinity of liquidus temperature or 650°C. Such a microstructure is superior to that not put in electromagnetic field and suitable for semi-solid forming. The convection in metal as forced by the electromagnetic field will cause the secondary branches of the primary dendrites to break off or burn out at root when the temperature is fluctuating violently, which is just the key reason why the number of crystal nuclei increases in the slurry and the microstructure becomes finer and more uniform.