Abstract: The α-Fe is considered as a promising candidate for structure material in fusion reactors, which may undergo mechanical degradation due to irradiation of hydrogen and helium atoms. The clustering behavior of hydrogen and helium atoms in α-Fe is an important concern in fusion materials research. Using density functional theory calculations, the stability of the HeH_n cluster and the trapping behavior of hydrogen atoms by a substitutional helium defect were investigated. And it shows that a helium atom can trap four hydrogen atoms at most, and the trapped hydrogen atoms tend to sit neighboring octahedral sites. The trapping energy of hydrogen atoms implies that HeH₄ is the major structure in α-Fe when hydrogen atoms are abundant, and HeH₂ predominates otherwise.