The single crystal of calcium nitriminotetrazolate pentahydrate [Ca(NATZ)(H₂O)₅], a novel green initiating explosive was prepared by slow evaporation method. Its structure was characterized by a X-ray diffractometer. The crystal is triclinic, space group P1 with crystal parameters of a=0.64803(13)nm, b=0.74328(16) nm, c=1.0348(2) nm, α=74.482(8)°, β=72.487(9)°, γ=74.755(9)°, V=0.44888(16) nm³, Z=4, D_c=2.050 g·cm^-3. On the basis of the structure characteristics of Ca(NATZ)(H₂O)₅, its decomposition mechanism was studied. The full optimized geometry and orbital energy analysis of Ca(NATZ)(H₂O)₅ were performed with the HF6-311G and B3LYP-6-311G methods using the Gaussian 03 program. Its thermal stability was studied. Rusults show there are two steps in its thermal decomposition which is agreed with expriments.