Abstract: Al-20% Si alloy was prepared by semi-solid casting using serpentine channel with spoiler. The effect of casting temperature on the microstructure and mechanical properties of Al-20% Si alloy was studied. The flow state of the alloy slurry in the channel was simulated using finite element software. The results indicate that the microstructure of Al-20% Si alloy consists of two phases: primary Si and Al-Si eutectic phase. The average size of primary Si in Al-20% Si alloy prepared by serpentine channel with spoiler is smaller than that without spoiler. As the casting temperature decreases from 730 ℃ to 700℃, the average size of primary Si grains gradually decreases, and the tensile strength and the elongation of Al-20%Si alloy gradually increase. At a pouring temperature of 700 ℃, the average equivalent diameter of primary Si in Al-20% Si alloy is 22.4 μm, and the tensile strength is 314.2 MPa. During the pouring process, the serpentine channel and the turbulence plate exert a dual stirring effect on the alloy slurry, increasing the nucleation number of primary silicon in the alloy, finally, the primary Si grains in the Al-20%Si alloy are refined.