Currently,　conductive　hydrogels　have　received　great　attention　as　flexible　strain　sensors.　However,　the　preparation　of　such　sensors　with　integrated　stretchability,　transparency,　and　self-healing　properties　into　one　gel　through　a　simple　method　still　remains　a　huge　challenge.　Here,　a　fully　physically　crosslinked　double　network　hydrogel　was　developed　based　on　poly(hydroxyethyl　acrylamide)　(PHEAA)　and　κ-carrageenan　(Car).　The　driving　forces　for　physical　gelation　were　hydrogen　bonds,　ion　bonding,　and　electrostatic　interactions.　The　resultant　PHEAA-Car　hydrogel　displayed　stretchability　(1145%)　and　optical　transparency　(92%).　Meanwhile,　the　PHEAA-Car　hydrogel　exhibited　a　self-healing　property　at　25　°C.　Additionally,　the　PHEAA-Car　hydrogel-based　strain　sensor　could　monitor　different　joint　movements.　Based　on　the　above　functions,　the　PHEAA-Car　hydrogel　can　be　applied　in　flexible　strain　sensors.