The unique substitution reactions of the three-membered-ring silylenoid H2SiLiF with GeH3X (X = F, Cl, Br) were investigated using ab initio and density functional theory calculations. All stationary points on the potential energy surfaces were optimized at the B3LYP/6-311 + G (d, p) level of theory and the QCISD method was then used to calculate the single-point energies. Theoretical calculations predicted that the substitution reactions of H2SiLiF with GeH3X proceed via two reaction paths (I and II), while forming the same product H2FSi-GeH3. In either pathway, there is one precursor complex (Q), one transition state (TS), and one intermediate (IM) connecting the reactants and products. The substitution reaction barriers of H2SiLiF with GeH3X for path I (48.49, 42.71, and 38.71 kJ mol(-1)) decreased with the increase for the same-family element X from up to down in the periodic table, whereas the substitution barriers for path II (6.51, 22.04, and 23.62 kJ mol(-1)) increased with the increase in atomic number of X (X = F, Cl, Br). Path II was more favorable than path I. All the substitution reactions of H2SiLiF with GeH3X were exothermic. The elucidation of the unique mechanism of these substitution reactions suggests a new reaction mode of silicon-germanium bond formation.