By using DFT method of quantum chemistry, the tetraamminediazido cobalt(Ⅲ) perchlorate（DACP) molecule structure parameters were calculated. The DACP structural characteristics, spectrum performance and photochemical decomposition mechanism were analyzed. Results show that the nucleophilic center was N,atom in NH₃ and N₃, the electronic center was Cl in ClO₄ and Co atoms. The DACP outside electron was moved from N atom in —N₃ to Cl atom in —ClO₄. The transition energy was divided into many levels. there was sequence absorbing peaks in the range of 340.99-699. 89 nm. The DACP theory IR spectra were calculated at BLYP/DNP level. The results of calculation on IR were essentially consistent with experimental values.