The modified ammonium nitrate(AN) was prepared by adding more than 20 kinds of inorganic additives with dosage of 0.99%(wt), and the effects of these additives on AN polymorphs were studied by differential scanning calorimetry (DSC) method. The results show that potassic salts prevent the transition of Ⅳ-Ⅲ effectively, while oxide, Cu(NO₃)₂, (NH₄)₂SO₄ and MgSO₄ prevent the transition of Ⅲ-Ⅱ, the composite of KCl and ZnO prevent the transition of Ⅳ-Ⅲ and Ⅲ-Ⅱ simultaneously. The effects of inorganic additives on AN phase transition are the coaction of such factors as anion and cation radius and their matching, ion substitution, the form of solid solutions, adulteration, solubility, charges, ion stereostructure etc.