Stereoisomerism plays a unique role in tuning the structures and performances of energetic molecules. Photochemical reactions feature mild conditions and precise configurational regulation thus bear important theoretical and practical significance for realizing stereoisomeric transformation of energetic molecules. (E)-Potassium 5,5'-azotetrazolate (E-PZT) was employed as the substrate in this work. Systematic condition screening was conducted to determine the optimal parameters for the photochemical synthesis of (Z)-potassium 5,5'-azotetrazolate (Z-PZT). The molecular structure of Z-PZT was fully characterized. The half-life of Z-PZT is measured to be 49 min at room-temperature. Theoretical calculations highly consistent with the experimental phenomena and results of the photoinduced isomerization reaction. The predicted excitation wavelengths and corresponding spectra obtained from theoretical calculations are highly consistent with the experimental phenomena and results of the photoinduced isomerization reaction. The successful preparation of the target product Z-PZT is further verified by these theoretical results. The isomerization energy barrier was calculated, and a rational photochemical reaction mechanism was accordingly proposed to elucidate the metastable characteristic of Z-PZT and the intrinsic origin of its relatively short half-life. Reliable experimental and theoretical support is provided by this work for the investigation of photoinduced isomerization regulation in energetic molecules.