Abstract: The sodium alginate-silica/polyacrylic acid (SA-SiO₂/PAA) composite hydrogel powder was prepared for adsorption of ammonia nitrogen in water and was characterized by FTIR, XPS, SEM-EDS, BET and ζ potential. FTIR and SEM-EDS characterization results show that SiO₂ is successfully compounded into the hydrogel. The BET characterization results indicate that the specific surface area of the adsorbent is 2.689 m²·g⁻¹, the total pore volume is 0.007 cm³·g⁻¹, and the average pore size is 10.35 nm. The ammonia nitrogen adsorption experiment results show that the adsorption of ammonia nitrogen on the SA-SiO₂/PAA composite hydrogel conformed to the pseudo second order kinetic model. The Langmuir adsorption isotherm model fits the adsorption behavior of the SA-SiO₂/PAA composite hydrogel better, and the maximum adsorption capacity is 83.29 mg/g according to the Langmuir model. When the initial concentration of ammonia nitrogen in the solution is 200 mg/L, the initial pH value is 9.0, the adsorbent dosage is 2.5 g/L, and the adsorption time is 80 minutes, the adsorption effect is the best, at equilibrium, the adsorption capacity is 37.4 mg/g. The research results indicate that the main adsorption mechanisms of ammonia nitrogen are electrostatic interaction between carboxyl groups and NH₄⁺, hydrogen bonding, ion exchange and pore adsorption.