The results of investigation of sulfur hexafluoride decomposition in mixture with hydrogen and oxygen in plasma of pulsed electron beam formed by accelerator TEA-500 (350...500 kV, 60 ns, current density 0,3...0,4 kA/cm2) have been presented. The data of thermodynamic simulation of gas mixture SF6+O2 and SF6+H2+O2 conversion in low-temperature plasma and gas mixture composition after electron beam influence measured by mass-spectrometer are given. It is shown that the formed gas-cycle compound synthesized in plasma of pulsed electron beam is sulfur difluoride-oxide. Isotope analysis of (SOF)+ and (SOF2)+ ions is carried out. It is obtained that sulfur isotope 34S content in sulfur difluoride-oxide exceeds its content in initial sulfur hexafluoride in 1,8±0,1 time