Quadratic configuration interaction (QCISD) method has been used to optimize the possible ground-state structures of BH2 and AlH2 molecules. The results show that the ground state of BH2 molecule has C2v symmetry and is in the 2A1 state. The parameters of structure and the harmonic frequencies are RBH=0.1187nm, ∠HBH=128.7914°, De=3.65eV,ν1(a1)=1020.103cm-1,ν2(a1)=2598.144cm-1 and ν3(b2)=2759.304cm-1, respectively. The results also show that the ground state of AlH2 molecule has C2v symmetry and is in the 2A1 state. The parameters of structure and the harmonic frequencies are of RAlH=0.1592nm, ∠HAlH=118.095°, De=2.27eV,ν1(a1)=780.81cm-1,ν2(a1)=1880.81cm-1 and ν3(b2)=1910.46cm-1, respectively. The potential energy functions of BH2 and AlH2 have been derived from the many-body expansion theory. The potential energy functions describe correctly the configurations and the dissociation energies of the two ground-state molecules. Molecular reaction kinetics of BH+H and AlH+H based on the potential energy functions is discussed briefly.