A study on the synthesis of zeolite from coal fly ash from power plant was carried out to reduce environmental problems and reuse industrial waste. The synthesized zeolite was proved to be Zeolite 4A type by means of the XRD and SEM analysis, and then the synthesized zeolite was used as an absorbent to remove the $NH_4^+$ ions in the wastewater and water. In the ion exchange of single $NH_4^+$ ions by the natural zeolite and the synthesized zeolite, the ion exchange reached equilibrium within 10 min. and 1hr, respectively. The amount of ion exchanged $NH_4^+$ to the unit weight of natural zeolite and zeolite 4A were 1.09 and 3.54 meq/g respectively, and the amount of $NH_4$ ion exchanged by the synthesized zeolite was higher than by the natural zeolite. The ion exchange kinetics fitted very well to the Feundlich and Langmuir isotherm. The effects of coexisting cations on the ion-exchange properties of zeolites were studied in order to apply them to water treatment. In the bisolute-system of the $NH_4^+-K^+$ and $NH_4^+-Na^+$ systems, the ion exchange capacity was smaller than the single $NH_4^+$ ion system. The effects of coexisting cations on the ion exchange system by the natural zeolite and the synthesized zeolite were found to be $K^+>Na^+$ and $Na^+>K^+>>Mg^{2+}>Ca^{2+}$, respectively.