Abstract: Hydrogel materials are widely used in wearable strain sensors due to they have unique biomimetic structure, performances and biocompatibility. However, it is still a big challenge to prepare a hydrogel sensor with good mechanical properties and high conductivity. In this paper, a fully physically crosslinked, high-strength and sensitive polyacrylic acid-Al³⁺/chitosan composite double network hydrogel sensor was prepared by a simple two-step method. Firstly, chitosan (CS), polyacrylic acid (PAA) and ionic crosslinker Al³⁺ were physically mixed in water to form a pre-gel, and then the pre-gel was immersed in NaCl solution to prepare the target hydrogel sensor. The obtained ionized hydrogel sensor shows excellent mechanical properties (tensile strength as high as 765.4 kPa, elongation at break to 1025%, and toughness of 4.13 MJ/m³). At the same time, the strain sensor based on the hydrogel exhibits excellent tensile sensitivity (sensitivity factor is about 1.54). The hydrogel sensor can repeatedly and stably detect large and small strains of human body. Therefore, the introduction of physical cross-linking network through the action of metal salts can improve the performances of hydrogels, which providing a new perspective for the design of multifunctional materials and their applications in electronic skins, wearable devices, and biosensors.