The density function （B3P86） method has been used to optimize the possible ground-state structure of SiF2 molecule. The results show that the ground state of SiF2 molecule has C2v symmetry and its electronic ground state is X1A1. The equilibrium parameters of the structure are RSi—F=0.1061　nm and De=13.8 eV. On the base of atomic and molecular reaction statics, the reasonable dissociation limit for the ground state of SiF2 molecule is determined. Then the analytic potential energy function of SiF2 molecule is derived by many-body expansion theory. The potential curves describe correctly the configurations and the dissociation energy for the SiF2 molecule.