The invention relates to a method for preparing a ZnO film by a two-step deposition method and a device thereof, belonging to the technical field of nano-crystal film preparation methods. The method is characterized in that principles and equipment of ultrasonic atomization pyrolysis and sol-gel method are comprehensively utilized to deposit the ZnO film in two steps; the first step is to prepareZnO nano-particles by improved ultrasonic atomization pyrolysis equipment; the equipment is mainly characterized in that a high-pressure generation source and a charging nozzle are additionally arranged to a spray conduit, and a quartz pipe passes through the whole heating furnace, so that the particles are directly introduced to a beaker filled with a certain amount of deionized water; and in the second step, the ZnO nano-particles are repeatedly cleaned by an ultrasonic cleaner and a centrifugal machine, and are finally applied to a substrate by a spinning coater. By adopting the method, environmental pollution of aerosol generated in the ultrasonic atomization pyrolysis preparing process can be avoided, and the ZnO film with high crystal quality can be obtained.