Using the QCISD/6-311++G(3df,3pd) and B3P86/6-311++G(3d2f) respectively, the possible ground-state structures of SiH2 and SiF2 molecules have been optimized. The results show that the ground state of SiH2 molecule is of C2v symmetry and in the 1A1 state, whose angle, equilibrium nuclear distance and dissociation energy are 92.5025°, 0.15149nm and 3.7098eV, respectively, The results also show that the ground state of SiF2 molecule is of C2v symmetry in the 1A1 state, whose angle, equilibrium nuclear distance and dissociation energy are 100.7079°, 0.16014nm and 14.1391eV, respectively, and their harmonic frequencies and force constants have been calculated. The present paper correctly determines the dissociation limits based on group theory and atomic and molecular reactive statics (AMRS). Analytical potential energy functions for the ground states X1A1 of SiX2(X=H，F) have been derived using many-body expansion method. The structure and energy of SiX2(X=H，F) can correctly reappear on the potential surface. Molecular reaction kinetics of SiH+H and SiF+F based on the potential energy functions is discussed briefly.