TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: The enriching step comprises gradually improving concentration of matrix ammonia and nitrogen, in which initial concentration of cultivation liquid ammonia and nitrogen during cultivation is 100-600 mg/l, final ammonia and nitrogen concentration is 700-2000 preferably 1000-1500 mg/l, chemical oxygen demand (COD) value of cultivation liquid is less than 400 preferably less than 200 mg/l, and initial concentration of ammonia and nitrogen is reduced at less than 150 mg/l while concentration of matrix ammonia and nitrogen is improved; filling carbon source so that COD concentration of cultivation liquid is not less than 100 mg/l, and ammonia and nitrogen concentration is improved to 50-400 mg/l for each time; and enriching at 20-40 degrees C and pH of 6-9 preferably 6-8 until dissolved oxygen is more than 2 preferably 2-10 mg/l. The cultivation step comprises controlling dissolved oxygen at less than 0.5 mg/l, COD value of cultivation liquid of more than 400 mg/l, and ammonia and nitrogen concentration of cultivation liquid is 700-2000 mg/l. The primary sieving uses solid substrate containing nitrate and nitrogen, while secondary sieving uses solid substrate containing ammonia and nitrogen. The step of domesticating growth capability on purified heterotrophic nitrobacteria can be performed by carrying out gradient domestication via gradually reducing good quality carbon source and gradually improving bad-quality carbon source; and selecting partial flora from solid flat plate using bacteria receiving ring to inoculate in reactor contained with cultivation liquid to cultivate; in which concentration of initial nitrogen source counted based on nitrogen oxide nitrogen (NOx- and -N) is 50-200 mg/l, and concentration of initial carbon source counted based on COD is 500-5000 mg/l; detecting concentrations of nitrogen source and carbon source in cultivation liquid; controlling mass ratio of carbon source to nitrogen source in reaction system during domesticating growth capability at (3:1)-(20:1); filling carbon source if carbon source is insufficient and filling nitrogen source if carbon source is insufficient; and ending reaction until total nitrogen and COD concentration are respectively lower than 15 mg/l and 60 mg/l. The domestication cultivation is performed at 20-35 degrees C, pH of 6.5-9.8 preferably 7-8.5, and dissolved oxygen of 0.05-5 preferably 0.2-1 mg/l. The step of domesticating denitrifying capability is performed by transferring, replacing water or filling bacteria in batches, in which concentrations of nitrogen source and carbon source are gradually improved; and concentrations of nitrogen and carbon in wastewater to be treated are obtained. The wastewater to be treated can also be directly used for carrying out domestication on denitrifying capability such that during domestication, temperature is at 20-35 degrees C, pH is 6.5-9.8, and different dissolved oxygen and COD concentration conditions are given, thus domestication is performed on bacteria. Preferred Component: The good-quality carbon source is sodium succinate, glucose, sodium citrate, sodium acetate, or ethanol. The bad-quality carbon source is industrial methanol, industrial waste ethanol or high-concentration COD sewage.