Stimuli-responsive hydrogels are becoming increasingly important for controlled drug delivery, biosensing, and tissue engineering. However, few pH-sensitive hydrogels with good mechanical property have been extensively reported. In this investigation, we reported the preparation of extremely stretchable and tough pH-sensitive hydrogels by introducing a linear polysaccharide-agar into the poly(acrylamide-co-acrylic acid) (P(AM-co-AA)) network and using diacrylated PEG (PEGDA) as a chemical crosslinker based on a simultaneous interpenetrating polymer networks (IPN) structure. It was found that longer PEGDA chains would lead to the obvious increase in swelling ratio and the stretchability of hydrogels. Moreover, the content of agar, the crosslinker concentration and the pH of the external environment would significantly affect the mechanical characteristics of the hydrogels. The compression strength and dissipated energy could reach 4.56 MPa and 0.56 MJ m⁻³ under the deformation of 85%, respectively. Also, hydrogels exhibited excellent reversible swelling and recoverable deformation. The improved mechanical properties enable the pH-sensitive hydrogels to be potential candidates in the field of load-bearing soft tissues.