The invention relates to the technical field of energy sources, in particular to a Brayton cycle system and a flow for zero emission of carbon dioxide (CO2) by utilizing liquid hydrogen (LH2) condensation. The system is formed by coupling a semi-closed and regenerative Brayton cycle and a liquid hydrogen (LH2) gasification unit, the liquid hydrogen gasification unit is taken as a low-temperature cold source of the semi-closed and regenerative Brayton cycle so that the condensation process obtains a low temperature far lower than an ambient temperature. The Brayton cycle adopts a nitrogen working medium and a hydrogen fuel without CO2 generation during the combustion; therefore, the zero emission of various environment-harmful pollutions comprising the CO2 is realized under the condition of no need of additional energy consumption. At the same time, relative to the prior Brayton cycle with the nitrogen working medium which takes the environment as the cold source, the thermodynamic property of the Brayton cycle system is greatly improved, so the Brayton cycle system has good economical efficiency and broad engineering application prospect.