Borax-PVA hydrogels with excellent mechanical properties are prepared by simple physical mixing of polyvinyl alcohol (PVA, thickener) and borax (cross-linking agent) at room temperature. The resulting hydrogel is a three-dimensional structure composed of boric ester bonds as physical crosslinking points. Thus, the spatial structure, swelling properties, viscoelastic properties, tensile properties, and self-healing properties of hydrogels with different ratios of borax and PVA are studied. XRD confirmed that the hydrogels have similar structures near 2θ values of 10 and 20. The microstructure of the hydrogel is confirmed by SEM and TEM. With an increase of borax mass fraction, the pore structure and morphology of hydrogel are more ordered, with substantial quantities of water immobilized within their three-dimensional structure. The viscoelastic properties and tensile properties showed that when the mass fraction of borax is 5%, the storage modulus and compressive stress of the hydrogel are the highest, reaching 100 Pa and 5.6 kPa, respectively. In addition, through physical and chemical stimulation (heating and varying pH, respectively), the hydrogels also showed reversible gel–sol conversion characteristics, indicating that the boric ester bonds have self-healing properties.