A sleeve-type mechanically stirred ammonium magnesium phosphate crystallization-inclined plate enhanced precipitation reactor was developed to treat wastewater containing high concentration of nitrogen and phosphorus, and recover ammonium magnesium phosphate crystals. The effects of stirring speed, hydraulic retention time and total number of particle collisions (GT value) on reactor performance were investigated. The computational fluid dynamics software (Fluent 18.1) was used to conduct numerical simulation of the flow pattern in the reactor, and the rationality of reactor structure design was analyzed. This would provide technical reference for the design and operation of the ammonium magnesium phosphate crystallization-precipitation reactor. The results indicated that the average recovery of ammonia nitrogen and phosphorus was above 76.00% and 97.00%, respectively, when the stirring speed was 250r/min, the hydraulic retention time was 0.375h, and the average GT value was from 14,000 to 20,000. Under such operating conditions, the average particle size of crystal reached 20.515μm, and the turbidity of effluent was below 2NTU. The results of scanning electron microscopy and X-ray diffraction showed that the precipitate in the reactor was pure magnesium ammonium phosphate. There was an obvious hydraulic grading in different areas of the reactor, with a turbulent flow pattern in the mixed reaction crystallization zone, a transition flow regime in the buffer zone and the collecting zone of magnesium ammonium phosphate, and a laminar flow pattern in the solid-liquid separation zone. The flow characteristics of the reactor showed that its structural design could meet the hydraulic requirements for crystal formation and growth as well as the solid-liquid separation under suitable operating conditions.