The article states that the mechanism of the fusion reaction of deuterium and tritium nuclei is not completely clear. The overwhelming majority of modern thermonuclear reactors and their projects are focused on the use of deuterium–tritium plasma. It has been established that the mechanism of fusion of deuterium and tritium nuclei differs from the classical mechanism of a compound nucleus proposed by N. Bohr and from the direct interaction proposed by S. T. Butler. The article proposes a new mechanism that assumes the formation of a compound nucleus of helium-5. Unlike the Bohr mechanism, in the proposed model the compound nucleus 5He formally refers to a non-existent one. Its average lifetime is about 7 × 10–22 s and is comparable with the characteristic time of strong interaction (τS ~ 10–23…10–22 s). The reaction rate is typical for direct nuclear interactions, and the sequence of events, the mechanism and the dependence of the cross section on the energy of the interacting nuclei are typical for nuclear reactions realized through the formation of a compound nucleus. Thus, a new mechanism of the fusion reaction has been revealed. An overview of thermonuclear reactors is presented.