An all-soft, highly stretchable liquid metal (LM) conductor with high electrical conductivity, excellent electrical conductivity stability under various mechanical deformations and good mechanical properties was achieved. The stretchable conductor was prepared by infiltrating Gallium-indium-tin (GIT) LM into porous polyurethane sponge (PUS) with large porosity and small pores using a vacuumizing method followed by encapsulation with Polydimethylsiloxane (PDMS) to prevent the leakage of GIT-LM and to improve the mechanical properties. The as-made PDMS/PUS/LM composite shows a high tensile strength (1.11 MPa), high elongation at break (419%), excellent electrical conductivity (104 S/cm) and electrical conductivity stability under various mechanical deformations. The normalized resistance is of highly repeatability in stretch-release and bend-release cycle experiments.