The invention provides a preparation method of a battery diaphragm. The preparation method comprises the following steps: S1, coating a ceramic coating solution containing a hydrophobic substance on abase membrane under a light shielding condition to obtain a ceramic diaphragm; S2, covering the ceramic diaphragm obtained in the step S1 with a mask with a pattern, and carrying out ultraviolet irradiation to obtain a ceramic diaphragm with a hydrophilic part and a hydrophobic part; and S3, coating the ceramic diaphragm obtained in the step S2 with the polyvinylidene fluoride dispersion liquid.By adding a hydrophobic substance into a ceramic formula, the problems of hole blockage and needle blockage during spraying are solved. PVDF dot matrix coating can be achieved only through a traditional coating mode, so high-price equipment is not used, and cost is reduced. The performance of the product is equivalent to or better than that of the existing dot matrix PVDF diaphragm, so that the market requirement is met. The method is simple and easy to implement, and the dot matrix PVDF coated diaphragm can be produced on a large scale.