The Radial Forging Combined with Unidirectional Compression Recrystallization and Partial Melt (RFCUC-RAP) and Radial Forging Combined with Multi-axial Compression Recrystallization and Partial Melt (RFCMC-RAP) were proposed to prepared semi-solid billet. The microstructural evolutions of semi-solid 6063 Al alloy prepared by direct semi-solid isothermal treatment (SSIT), RFCUC-RAP and RFCMC-RAP were investigated. Results show that, the solid grains of semi-solid billet prepared by direct SSIT are large. However, solid grains of semi-solid billet prepared by RFCUC-RAP and RFCMC-RAP are fine and spherical. Additionally, the RFCUC-RAP is superior to the RFCMC-RAP owing to the relatively simple deformation process, which is an effective method to prepare high-quality semi-solid billet.