The adsorbent of modified bamboo charcoal crosslinking chitosan copper was optimized by making modified bamboo charcoal and crosslinking chitosan copper under 5% sodium alginate to remove ammonium in low temperature and low turbidity water. The physico-chemical properties of the as-prepared modified bamboo charcoal crosslinking chitosan copper, such as morphology, structure, surface area, and chemical composition were characterized by SEM, IR and BET. The adsorption capability and rules of NH3-N in aqueous solutions were tested in the static system. Adsorption mechanism of ammonium on modified bamboo charcoal crosslinking chitosan copper had been studied by DFT Simulation. The results showed that the adsorption optimum conditions were pH value of 8, ammonium concentration of 5 mg/L, temperature of 5 ℃, and stirring speed of 165 r/min, adsorbent amount of 1 g/L, the removal rate was over 80%. The specific surface areas of modified bamboo charcoal crosslinking chitosan copper were 157.78 m2/g,in the main of micropore adsorption,which made up to over 90% of total pores. The six membered ring of the amine portion on crosslinking chitosan copper were strengthen and stable. Hydroxide radical, amino of chitosan reacted with “d” orbit of copper, forming stable mesh unit structure; the reason of the ammonium removal lied in that ammonium reacted with copper to form copper ammonia complex ion. The adsorption kinetics of NH3-N by modified bamboo charcoal crosslinking chitosan copper followed the pseudo-first-order model. Density functional theory(DFT)showed that the synergistic effect of bamboo charcoal not only enhanced the adsorption capability of NH3-N, but also promoted the stable of adsorption.