To investigate the effect of composite structure on the mechanical properties of composite yarns, aramid/ recycled PET (r-PET) composite yarns were prepared by aramid with r-PET yarns in the form of wrapping, combining paralleling and ply-twisting. The microstructure and mechanical properties of the resulting aramid/r-PET composite yarns were characterized by using scanning electron microscopy and a universal material testing machine. The results showed that the wrapping method was not effective in enhancing the mechanical properties of r-PET yarns. The breaking strength of the parallel method reached 12.32 cN/dtex, and the breaking strength was up to 328.96 N. When the twist rate was 250 T/M, the breaking strength of the composite yarns obtained by the combined strand ply-twisting method was up to 13.47 cN/dtex, and the breaking strength was up to 348.88 N, which was the best composite effect.