A novel method of “fully covered + friction stir welding + accumulative roll bonding” was developed to prepare an Al/Mg/Al laminated composite material (LCM). This work presents a rolling simulation of an Al/Mg/Al LCM using the DEFORM software and processing maps to show the hot rolling mechanism. The single pass reduction should be set at approximately 3–4 mm by finite element simulation. The edge damage value of the core Mg alloy plate in the Al/Mg/Al LCM decreased with the increasing hot rolling temperatures. The optimum process parameters were obtained by processing maps for deformation temperatures from 250 °C to 300 °C and 350–400 °C in the strain rate range of 0.01 s−1 to 0.1 s−1. The hot rolling temperature for the 11.5 mm-thick Al/Mg/Al LCM should be controlled at 400 °C, and the single pass processing rate should be selected in the range of 20–40%. With each increase in heat treatment temperature and time, the compound gradually increased, and the thickness of the transition layer gradually increased at the Mg/Al interface. The growth kinetic model formulas of the interface layer for the 1060/AZ31/1060 LCM under different rolling strain fields were obtained, which could have been predicted by the interface layer thickness at different rolling reduction rates and heat treatments.