The high concentration ammonia nitrogen wastewater from Fushun Catalyst Plant was treated by single factor experiment and orthogonal experiment with magnesium ammonium phosphate method. The results were fitted and optimized by penalty function method and Gauss Newton method. The results of orthogonal experiments show that n(Mg)/n(N) has the greatest influence on the removal rate of ammonia nitrogen, followed by pH, while n(P)/n(N) has the least influence. The fitting curve was obtained by Gauss Newton method, and the optimal reaction conditions were determined by penalty function method: n(Mg)/n(N)=1.30,n(P)/n(N)=1.26, pH=9.59. Under the process condition, the removal rate of ammonia nitrogen is 99.79%, and the mass concentration of residual ammonia nitrogen is 28.33 mg/L, which meets the secondary standard of sewage discharge.