The invention discloses aqueous metal ion pentazole salts and a preparation method thereof. The metal salts have a chemical structural formula of M(N5)x(H2O)y. When M represents a monovalent metal Li, Na, K or Ag, x is 1 and y is 4. When M represents a divalent metal Fe, Co, Ni, Mg, Ca, Ba, Cu, Zn or Pb, x is 2 and y is 8 or 10. The preparation method utilizes metachloroperbenzoic acid and ferrous glycinate as a cleavage reagent and an aid acting with aryl pentazole. Through an oxidative cleavage method, the C-N bond of the aryl pentazol molecule is selectively cut and a metal ion-containing salt is used as a capture reagent in preparation of the aqueous metal ion pentazole salts. The preparation method successfully prepares the metal pentazole salts. The metal pentazole salts can be widely used in the field of energetic materials.