In the paper, plasma discharge in a liquid flow at high pressure for use in producing hydrogen gas has been carried out. Methods and equipment for plasma discharge excitation in a liquid medium flow have been developed by the authors. The liquid flow has been directed at excess pressure to the hydrodynamic radiator located at the reactor inlet where an ultrasonic two-phase vapor-liquid flow has occurred at lower pressure due to the pressure difference and decrease in the flow enthalpy. Electric field which intensity exceeds the breakdown threshold of this two-phase medium is generated between electrodes located in the reactor by an external power supply, thus resulting in excitation of the low temperature quasi-steady plasma glow discharge. Theoretical estimation of the parameters of such discharge has been carried out by the authors. It is shown in the paper that low temperature plasma initiated under the conditions of a liquid-phase medium flow in the discharge gap between electrodes could effectively split hydrogen-containing molecules of organic compounds in a liquid with formation of gaseous products having hydrogen content of more than 90%. In addition, theoretical calculations of the discharge voltage and current which are in good agreement with the experimental results have been carried out in the process simulation. With a mixture of oxygen-containing organic compounds as a raw material, the output capacity of the 50 mL reaction system used in experiments has been around 1.5 l of hydrogen per minute. Decomposition of those compounds in plasma may also result in formation of some solid-phase products, such as carbon nanoparticles and nanoparticles of the discharge electrode oxide materials. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.