The invention provides a deep denitrification process for wastewater. The deep denitrification process comprises the following specific steps of: firstly, performing microwave irradiation and coagulating sedimentation on the wastewater, wherein a certain quantity of NaOH is added into the high-concentration ammonia-nitrogen wastewater to adjust the pH value of the wastewater to 11-13, and a flocculant and a coagulant are added into the wastewater at an alkaline condition to perform the coagulating sedimentation, thus obtaining supernatant liquor; secondly, introducing the supernatant liquor obtained in the first step into an air stripping tower, wherein a sprayer is arranged at the top of the air stripping tower, multiple packing layers are arranged in the middle in a tower body, after passing through the sprayer, the wastewater becomes fine flow and flows through the packing layers, an air blower introduces air into the tower through an aeration port at the bottom of the tower, the air is in contact with the fine flow on the surface of packing, and exhaust for air stripping enters an absorption cell containing waste hydrochloric acid or waste sulphuric acid absorption liquid to absorb a part of ammonia nitrogen; thirdly, performing continuous circulating ammonia sedimentation on pyrolysis products of magnesium ammonium phosphate (MAP), and after the sedimentation of the MAP, processing effluent by a biological nitrogen removal process; fourthly, performing anaerobic (A)-anoxia (4)-oxic (O) biological nitrogen removal process on the effluent in the third step; and fifthly, performing denitrification on the left less nitrogen by a denitrification biofilter and a membrane filter. Therefore, ammonia nitrogen and total nitrogen of the effluent of the processed wastewater can reach a first-level A standard in the discharge standard of pollutants for municipal wastewater treatment plants (GB18918-2002).