The invention relates to the technical field of waste water treatment, in particular to a treatment method of high-concentration ammonia nitrogen waste water. The treatment method comprises the steps of adding alkaline liquor into the waste water, uniformly mixing, then adding fresh magnesium salt and phosphate liquor, settling, filtering, flushing and refiltering a settling product, drying and pyrolyzing the settling product, recovering a half of a pyrolyzed product to a mixing reaction tank, acidolyzing the other half of the pyrolyzed product continuously, recovering a solution after re-acidolysis to the mixing reaction tank, circulating for many times, then metering in the reaction tank, adding an appropriate amount of the magnesium salt and phosphate liquor, and allowing ammonia generated during treatment to react with an acidic solution to form ammonia salt. The invention further relates to a treatment system employing the method for treating the waste water. The treatment system comprises the mixing reaction tank, a settling tank, an aerobic catalytic oxidation tank, a filtering and flushing tank, a drying pyrolyzer, an acidolysis tank and an acidic solution absorption tank. The method realizes cyclic utilization of an agent, and saves the acidic solution. The treatment system is simple in structure and convenient to mount and operate.