The crystal of tetrammine-cis-bis(5-nitro-2H-tetrazole-N²) cobalt (Ⅲ) perchlorate dihydrate was obtained and structurally characterized by applying Xray singlecrystal diffraction. Due to the presence of the two water molecules,a great amount of hydrogen bonds were formed,which linked the molecules together to a threedimensional neat structure,and the packing method various a lot contrast to the anhydrous BNCP.