Selective capture and direct recovery of silver ions from highly acidic wastewater are desirable but challenging for sustainable remediation of contamination. In this work, contraposing the characteristics of actual Ag-polluted water, poly-allylrhodanine (PAR) is designed and synthesized as an adsorbent. Different from most reported adsorbents, PAR features a unique acidity-enhanced adsorptivity property, thus achieving an ultrahigh capacity (651.0 mg g⁻¹) and outstanding selectivity (>100) in the capture of Ag⁺ from wastewater with strong acidity (pH −0.2). Moreover, the purity of the reclaimed Ag⁺ reaches up to 99.80%, delivering an enormous economic benefit. Further characterization and theoretical calculations uncover that the CS and C–S groups on PAR act as adsorption sites to coordinate the Ag⁺ ions via a special pH-dependent protonation exchange mechanism. In the treatment of actual Ag-polluted water, the treatment capacity of PAR is as high as 4015 bed volumes (BV) per run at pH = −0.2, which is 100-fold higher than that of commercial resin, highlighting its great potential in practical applications. The wastewater feature-directed design concept and the high-performance adsorbent of PAR reported in this work may be helpful to fill the gap between the experimental laboratory and practical remediation of Ag-containing wastewater.