Abstract: The mechanism and potential energy profile of the addition reactions between digermene (H₂Ge=GeH₂) and several nucleophilic reagents (CH₃OH, C₄H₉OH, PhOH and CF₃OH) were studied by using density functional theory (DFT), and the addition reactivity of these reagents was explored. The computed results show that the addition reactions between H₂Ge=GeH₂ and monomer of CH₃OH, C₄H₉OH or PhOH can occur in two different ways, i.e., nucleophilic addition and electrophilic addition, and electrophilic addition is relatively easier to happen. However, the addition reactions of H₂Ge=GeH₂ with dimer or trimer of CH₃OH can proceed only by nucleophilic addition. The reactivity of the CH₃OH dimer as a nucleophile is higher than that of the corresponding monomer, but the addition activity of the C₄H₉OH dimer is lower than that of the monomer. The order of reactivity of CH₃OH, C₄H₉OH, PhOH and CF₃OH as nucleophilic reagents from high to low is as follows: CH₃OH > C₄H₉OH > PhOH > CF₃OH.