The invention relates to a deaminizing agent and a preparation method thereof. The preparation method comprises the following steps: mixing and molding aluminosilicate and adhesive in the dry basis weight ratio of 90:10-70:30, and carrying out ion exchange with ammonium salt water solution to obtain the deaminizing agent. The deaminizing agent comprises the following raw materials in percentage by weight: 10-90% of SiO2, 5-10% of Al2O3 and 0.5-10% of MxO. The content of ammonia is greatly increased to higher than 10%, the degree of purification is lower than 0.3 ppm, the strength of adsorbentis very high, the phenomenon of efflorescence does not occur in the use process, and in addition, the adsorbent is reproducible and can be used for a long time.