Abstract: Multi-layer flexible and stretchable electronics have great potential in fields such as biomedicine, wearable devices, and electronic skin. However, the development and application of multi-layer flexible and stretchable electronics are hindered by issues such as poor conductivity, low stretchability, and difficulties in manufacturing interlayer interconnects. In this paper, a highly conductive stretchable composite material suitable for direct extrusion 3D printing of interlayer interconnecting wires was prepared by flexibly adding diethylene glycol (DEG) additives within the composite conductive materials of silver nanoparticles (AgNP), multi-walled carbon nanotubes (MWCNT) and polydimethylsiloxane (PDMS). Benefiting from the high melting point of diethylene glycol, the AgNP in the conductive composites can effectively aggregate and precipitate out of the surface during the curing process, thus improving the electrical conductivity. The good solvent wettability balances the issues of material structure collapse and 3D printer nozzle clogging, facilitating the 3D printing of interlayer interconnects. Meanwhile, the large aspect ratio of MWCNT can stabilize the electrical connection between AgNP during the stretching process. The resulting conductive material exhibits excellent conductivity (10⁴ S·cm⁻¹) and stretchability (cycling over 1000 times at 40% strain), which can achieve the printing of stretchable intralayer interconnects, self-supporting 3D vertical interconnects, and 2.5D curved interconnects based on material extrusion 3D printing technology. The stretchable composite paste developed in this study demonstrates good performance in flexible electrothermal heating and flexible display arrays, confirming the promising application prospects of stretchable conductive composite materials in the field of flexible and stretchable electronics, paving the way for the development of 3D printed multi-layer flexible and stretchable electronics.