mixing an oxidant and an organic ammonia-nitrogen wastewater in a catalyzation tank so as to dissolve the oxidant, wherein a ratio of said oxidant (Ox) to a chemical oxygen demand (COD) plus ammonia-nitrogen (Ox/(COD+ammonia-nitrogen)) is 0.1-30, and said oxidant is selected from a group consisting of potassium peroxymonosulfate (PMS) and a mixture of potassium peroxymonosulfate and persulfate;

processing said oxidant dissolved in said organic ammonia-nitrogen wastewater through a reaction selected from a group consisting of activation by applying ultraviolet (UV) illumination, catalyzation by adding a catalyst of a transition metal, and a combination thereof and simultaneously aerating the organic ammonia-nitrogen wastewater with a gas selected from a group consisting of air and oxygen so as to derive free radicals from said oxidant to simultaneously oxidize organic ammonia-nitrogen and other organic pollutants in the organic ammonia-nitrogen wastewater and obtain a processed solution, wherein a ratio of said catalyst of said transition metal to said oxidant is 0.00001-0.003, and said free radicals are active free radicals, comprising at least a selective free radical of SO₄−, a non-selective free radical of HO, and a superoxide radical of ROO; and

directing the processed solution to a neutralization tank to adjust a pH value of said processed solution.