Two-dimensional (2D) superconductors have important potential applications in constructing nano superconducting devices, thus, 2D superconductors with high critical temperature (Tc) are highly desired. Till now, the Tc of 2D superconductors are still relatively low. Based on density functional firstprinciples calculations, we predicted a new stable 2D transition metal molybdenum carbide 2H-Mo2C3. Based on the Eliashberg theory, we predict that it is not a superconductor. However, after hydrogenation, the hydrogen atoms increase the electronic density of states at the Fermi level, and strengthen the electron-phonon coupling. Accordingly, the hydrogenated 2H-Mo2C3, i.e., 2H-Mo2C3H2, is a 2D superconductor with Tc of 53 K, exceeding the McMillan limit. Thus, hydrogenation is an important strategy for obtaining 2D high-temperature superconductors at atmosphere pressure. In view of the high superconducting Tc of 2H-Mo2C3H2, it is highly expected to be synthesized in future experiments.