The invention provides a pretreatment method of ammonia-nitrogen wastewater. The pretreatment method of the ammonia-nitrogen wastewater comprises the steps that firstly, an appropriate quantity of denitrfying agents are added into high-concentration ammonia-nitrogen wastewater, then the solution is conveyed to an aeration tank of a denitrification tower through a pump, the denitrification tower is filled with a catalyst, and an air compressor carries out aeration treatment on the solution under the condition of pH>9 and at the temperature of 10-100 DEG C; the denitrfying agents are composed of methylcellulose, ethyl cellulose, sodium chlorite and citric acid, and the adding quantity of the denitrfying agents is 100 parts per million to 300 parts per million of the weight of wastewater. The pretreatment method of the ammonia-nitrogen wastewater is suitable for both inorganic ammonia-nitrogen wastewater and organic amine nitrogen wastewater, the TKN removal rate of high-concentration ammonia-nitrogen wastewater can reach above 85% after one time of treatment through the method, the organic amine nitrogen removal rate is above 90%, and a powerful guarantee is provided for subsequent biochemical treatment.