The invention discloses a method for preparing diamond-like carbon film (DLC), belonging to the metal or non-metal surface modification treatment technical field. The method adopts pulsed arc discharge by using graphite as a cathode electrode and a physically and chemically combined vapor deposition method for the decomposition and ionization of hydrocarbons gas to produce DLC deposition on a surface of a workpiece. The invention comprises the main operation steps of ultrasonic cleaning, vacuumizing, ion cleaning and DLC deposition, wherein argon gas is passed through in the ion cleaning step; a pulse frequency of the arc discharge in the DLC deposition step is 5 and 35Hz with voltage of between 200 and 400V; methane, ethane or propane are preferred as the hydrocarbons gas. A high-speed and high-energy carbon plasma ion beam is formed to generate collide decomposition and ionization to the passed through hydrocarbons gas through specific pulsed arc discharge to increase increasing density of the carbon ion and diffraction performance, thereby improving deposition speed and adhesive force of DLC, reducing internal stress, and improving precision and performance of DLC.