Uranium extraction from seawater is a promising strategy to alleviate global uranium scarcity, yet its implementation is hindered by extremely low concentrations and complex ionic environments. Concentrated seawater brine, a byproduct of salt production and desalination, contains 2-10 times more uranium than natural seawater, yet its high salinity presents additional challenges for extraction. Conventional polyamidoxime (PAO) hydrogels exhibit salt-induced shrinkage, compromising functional group accessibility and adsorption efficiency. Herein, we develop an anti-polyelectrolyte effect hydrogel by composing polyvinylphosphonic acid (PVPA) and the PAO. Under high-salinity conditions, cations and anions accumulate via diffusion around the positively charged amidoxime and negatively charged phosphonic acid groups, weakening interchain electrostatic attractions. This anti-polyelectrolyte effect promotes hydrogel swelling, significantly improving the exposure of binding sites and uranyl ion uptake. The PVPA-PAO hydrogel achieves a uranium adsorption capacity of 43.89 mg g⁻¹ after 24 days in concentrated natural seawater derived from solar saltworks, significantly surpassing that of previously reported PAO hydrogels (∼10 mg g⁻¹). In addition, it exhibits excellent antibacterial performance, mechanical robustness, and ion selectivity. This work presents an effective strategy for improving uranium recovery from marine resources and advances the comprehensive development and utilization of seawater resources.