In this work, ⁶⁰Co gamma-ray source was used to irradiate LLM-105 at room temperature with the radiation doses of 100, 300, 500, 696, and 900 kGy under vacuum. High-performance liquid chromatography coupled with electrospray mass spectrometry (HPLC–MS) and ¹H nuclear magnetic resonance (NMR) demonstrated the main radiolysis product in gamma-irradiated LLM-105 was 2,6-diamino-3,5-dinitropyrazine (ANPZ). The relationship between ANPZ content and irradiation dose indicated that LLM-105 was a stable explosive under gamma irradiation. The sensitivity is not expected to change based on the chemical analyses performed on irradiated LLM-105. The radiation decomposition mechanism of LLM-105 was clarified by Atomic dipole moment corrected Hirshfeld (ADCH) atomic charges and electronic localization function (ELF).