A preparation device has a chamber, molten metal containers, a rotatable base in the chamber and having a deposition substrate, laser sets generating a dual-pulse laser, a base controller and a data collection control unit. The containers communicate with the chamber and each has a pulse pressurization apparatus pressing the molten metal into the chamber. The laser sets correspond to the containers such that beams of an emitted dual-pulse laser bombard the pulsed droplets, plasmas are generated and are sputtered and deposited on the substrate forming a multi-element alloy thin film. The unit collects base temperature and displacement information, and controls the pressurization frequency of the pulse pressurization apparatus, and the emission frequency and energy of the dual-pulse laser of the laser sets controlling the frequency and energy of the dual-pulse laser bombarding the corresponding pulsed droplets. The base controller controls the base temperature, rotation and movement.