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To provide carbon steel a long-term corrosion protection effect in NaCl solutions with different pH values, based on poly-acrylamide (<i>PAM</i>) and oleate imidazoline (<i>OIM</i>), a solid corrosion inhibitor with the properties of pH-controlled release was synthesized. SEM, FTIR and TGA results indicated that the <i>OIM</i> inhibitors were successfully loaded into <i>PAM</i> hydrogel with a high <i>OIM</i> encapsulation content (39.64 wt.%). The <i>OIM</i> release behavior from the hydrogel structure has two stages, quick release and sustained release. The pH of solutions could affect the initial release kinetics of <i>OIM</i> inhibitors and the diffusion path in the hydrogel structure. Weight loss measurement of L80 steel in different pH solutions with <i>OIM@PAM</i> proved the inhibitor responsive release mechanism and anticorrosion performance. The inhibition efficiency of <i>OIM@PAM</i> can maintain over 80% after long-term immersion in a harsh corrosive environment (pH 3), which is much higher than the inhibition efficiency of <i>OIM@PAM</i> in a moderate corrosive solution.