The invention relates to a method for preparing a single c axial directional ZnO film through a modified electrochemical deposition technology, the method is characterized in that: electrochemical pretreatment process and constant current deposition are combined, to form a ZnO crystallon layer with a same size as a crystal point on a pretreated substrate surface, so that the subsequently deposition ZnO film has a single c axial growing property. The method more particularly comprises a preparation of electro-deposition initial solution, cleaning and treatment of the substrate and film growing; and finally an electrochemical deposition system is adopted for film growing. The prepared ZnO film layer has the single c axial direction, high crystallization degree, and rather high permeation rate in visible light area, which can be used as a window layer of a film solar energy battery and applied to such fields as piezoelectricity, optoelectronics and gas-sensitive sensor, etc. The method has low cost, does not need vacuum environment or using organism and high temperature heating equipment, and the method is applied to the preparation of large area and scale film materials.