Thixo-forming is in the forefront of metal processing technology in the 21st century. The research on thixo-co-extrusion of multi-layer tube as extension and development of the semi-solid forming technology is a completely new processing method for the composite material forming and is of great significance, in which different semi-solid billets (slurries) are extruded at the same time to form multi-layer tubes. In this study, different sizes of column-shaped and ring-shaped billets of Al/Mg alloys were firstly prepared by using specially designed molds. Then they were reheated by electric-resistance furnace，microstructures from different heating laws were investigated. Lastly, FEM simulation on thixo-co-extrusion of double-layer tube with A356/AZ91 was conducted.