The single crystal of tetraamminebis(5-nitrotetrazolato) cobalt (Ⅲ) perchlorate (BNCP) was prepared and characterized by elemental analysis and X-ray single crystal diffraction. The results prove that the crystal is monoclinic. Space group is P2(1)/n with crystal parameters of the unit cell dimensions: a=10.0149(11)Å,α=90°,b=10.5387(11)Å,β=109.0140(10)°,c=14.8241(16)Å,γ=90°,V=1479.2(3)ų,Z= 4,D_C=2.050 mg·mm³,μ=1.421 mm^－1,F(000)=928. The information is also provided about atomic coordinates,equivalent isotropic displacement parameters,bond lengths,bond angles and torsion angles of BNCP. On the basis of tested parameters,the structure characteristics and decomposed mechanism of BNCP were obtained.