Abstract The principle of reaction between magnesium and ammonium salt solution has many contradictory interpretations in high school chemistry. By determining the reaction rate of magnesium with different ammonium salt solutions, magnesium with different anion solutions and the volume of hydrogen generated, this paper obtained the essence of the reaction between magnesium and ammonium salt solutions:ammonium ion was a catalyst for magnesium reacting with water to form hydrogen; some anions (Cl-, SO42-) catalyzed the reaction of magnesium and water. Then this paper discussed the effects of ammonium salts on reaction of magnesium and water in terms of thermodynamics and kinetics.