The concentration of NH₄-N in the livestock solution is very high and toxic for the methanogenic bacteria to treat wastewater with anaerobic process. So, with MAP crystallization method, we search the MAP crystallization optimal condition to remove the NH₄-N in the wastewater to secure concentration(below 50 - 1000 ppm NH₄-N) and hope to set up the MAP crystallization process. We get the optimal NH₄-N removal efficiency at 30 rpm and high pH. The MAP sedimentation over the 90% is reached within 20min. The crystal size is over 0.05㎜ under the 40 rpm and pH 8. crystal form is like a rod and flower.