With the increasing awareness of environmental protection, the traditional insulating gas SF₆ is limited due to its high global warming potential, and the new environmentally friendly insulating gas HFO-1336 comes into being. It combines good insulating properties with low global warming potential, but it decomposes under certain conditions to produce harmful decomposition products such as HF and C3F8, which affect equipment operation and environmental safety. Therefore, it is crucial to select efficient adsorbent materials to adsorb these decomposition products, and MOF-74 series materials are ideal gas adsorbents due to their excellent pore size, specific surface area, and structural stability. In this study, we focused on Mn-MOF-74 to investigate its adsorption properties on HFO-1336 and its decomposition products HF and C3F8 based on density functional theory and giant regular Monte Carlo method using Material Studio software. The results show that the adsorption effect of Mn-MOF-74 on C3F8 is better than that of HF, the heat of adsorption of C3F8 is obviously higher than that of HF, and the sites occupied by C3F8 in the structure of adsorbed Mn-MOF-74 are more than that of HF, which provides a new idea and a new method for the effective adsorption and treatment of the decomposition product of HFO-1336, and also provides technical support for the development of environmentally friendly insulating gas application technology.