Primary steps of thermolysis of the promising high‐energy compound 1,1‐diamino‐2,2‐dinitroethylene (DADNE or FOX‐7) were studied by the quantum‐chemical methods using the PBE0 hybrid functional in the cc‐pVDZ basis set and the coupled‐cluster method at the CCSD/aug‐cc‐pVDZ level. A series of thermal decomposition reactions were studied. The reactions proceeding via hydrogen transfer from the amino group to carbon, along with four variants of transformations of the aci form of DADNE insufficiently studied earlier, are shown to be the most energetically favorable channels of the DADNE thermal decomposition. The activation enthalpies ΔHa of all these channels are close to the most reliable experimental values which are in the range of 190–200 kJ mol−1.