Chitosan is a natural macromolecule innoxious flocculant. Chitosan was protonated by sulfuric acid solution to enhance dephosphorization effect in wastewater treatment. The effect of protonation degree (pH value in sulfuric acid solution), adsorption time and pH value in raw water on dephosphorizing efficiency was researched. The results showed that bigger protonation degree can result in higher total phosphate removal rate (TPRR); TPRR was highest at 40~50 min of adsorption time; pH value in raw water had obviously effect on TPRR of protonated chitosan. TPRR decreased with pH value of raw water increasing when protonation degree was lower (pH ≥3 in sulfuric acid solution); TPRR was highest at pH = 6 in raw water when protonation degree was bigger (pH = 2 in sulfuric acid solution). The absorption process of protonated chitosan better fitted to pseudo-second order Lagergren equation and Langmuir absorption equation. Thermodynamics parameters of adsorption were ΔH<0, ΔG<0, and ΔS<0, adsorption behavior was exothermic, spontaneous and single molecular layer chemical adsorption process.