The mechanical property of diamond-like carbon films with different hydrogen concentration is studied using molecular dynamical simulation based on REBO potential energy functions. The stiffness, hardness, and elastic modulus of the films are calculated from the load-unload curve. It is shown that both of the fraction of sp3 carbon and the concentration of H in the films have strong influence on the film hardness. When H concentration in the film is lower than 39%, the hardness is mainly determined by sp3 carbon, when H concentration further increases, the hardness decreases greatly despite the increase of the sp3 fraction.