The mechanical properties of the molecular deposition film deposited on an Au substrate are studied in the theory for the first time. Firstly, the quantum mechanics have been used to calculate the structure parameters and potential parameters of the molecular deposition film. Secondly, molecular dynamics simulations have been used to study indent process of the molecular deposition film with the action of Au tip. The results showed that an obvious jump to contact appears during the An tip approaches the molecular deposition film; furthermore, the tilt angle and load of the molecules near the tip have the same tendency of hysteresis, which may be caused by the adhesive force between the tip and the molecular deposition film.