Fe base alloys are the most promising candidates for structural materials in the tritium breeding blanket and auxiliary tritium handling systems in fusion reactors.However,the irradiation damage,retention and permeation of hydrogen isotopes and hydrogen/helium embrittlement in structural materials under the nuclear environment are unavoidable engineering and technical problems.In the present work,the trapping behaviors of multiple H and/or He atoms in an Fe monovacancy have been investigated in the framework of first-principals calculations.