The invention discloses a preparing method and application of an ion selectivity cellulose-based adsorbent, and belongs to the field of light chemical engineering. According to the preparing method, cellulose is firstly introduced to carboxyl, and then carboxyl is connected to secondary amine in pyridone derivatives so as to prepare the modified cellulose adsorbent. The prepared modified cellulose adsorbent has low cost, a high adsorption capacity and stable adsorbability. Adsorbed heavy metal ions and dyestuff can be reutilized, thus the modified cellulose adsorbent has the huge advantages of energy conservation and emission reduction and environmental friendliness.