Insoluble dietary fiber (IDF) was extracted from watermelon peel and modified by hydrochloric acid. The adsorptions of nitrite by hydrochloric acid modified insoluble dietary fiber (HCl-IDF) and IDF were evaluated. The effects of pH value, oscillating temperature, HCl-IDF dosage, adsorption time, NO-₂ initial concentration on NO-₂ adsorption of HCl-IDF were tested. The results showed that the adsorption capacity of NO-₂ was doubled after modification. When the addition amount of HCl-IDF was 12.5g/L, the removal rate was 64.6% and tended to adsorption equilibrium. When the initial concentration of NO-₂ was 40mg/L, the adsorption was close to saturation. Increasing temperature, lowering pH and prolonging adsorption time were beneficial to the adsorption of NO-₂ by HCl-IDF, and the adsorption equilibrium was reached at pH 1.5,8K and 70min. The adsorption equilibrium of HCl-IDF for NO-₂ could be fitted by Langmuir isotherm equation, and the adsorption kinetics conformed to Langergren quasi-second-order kinetic model, which was mainly chemical adsorption. Thermodynamic studies showed that the adsorption of NO-₂ by HCl-IDF was an endothermic spontaneous reaction.