The generalized gradient approximation based on the density functional theory is used to study the adsorption process of H2O molecules by the Li decorated C6Li and the catalytic process of decomposition of H2O molecules. The geometry optimization shows that the most stable adsorption position of the Li is above the C atom of C6. Research shows that the adsorption of the first H2O molecule on C6Li needs to overcome an energy barrier of 1.77 eV, then H2O is decomposed into H and OH and bonding with Li atoms. Furthermore, the adsorption of the second H2O molecule needs to overcome an energy barrier of 1.2 eV and then the H2O molecule is decomposed into H and OH, the H atom in which and the H atom on the Li atom combine into an H2 molecule. OH replacing H atoms on Li atoms combines with the Li atom. Therefore, C6Li can be used as a catalyst for H2O molecules, and thus provide a new train of thought for the preparation of hydrogen storage material. The analysis shows that C6Li mainly adsorbs the H2O molecules through the dipole moment formed by the positive charge of Li and negative charge of H2O.