The invention discloses an electrostatic spraying device and a method for preparing micro-emulsified diesel fuel by the electrostatic spraying device. The electrostatic spraying device comprises an injection pump, a stainless steel needle, a high-voltage direct current power supply, a grounding copper ring, a product container and a magnetic stirrer, wherein distilled water flows out through the stainless steel needle via the injection pump the according to a certain flow speed; the high-voltage direct current power supply applies high-voltage static to the stainless steel needle; a high-voltage static electric field is formed between the high-voltage direct current power supply and the grounding copper coil; mixed liquid of the diesel fuel and functional composite emulsifiers is contained in the product container; the mixed liquid is uniformly mixed under the low-speed stirring of the magnetic stirrer. The distilled water forms electrostatic spraying under the effect of a high-voltage electrostatic field; after being atomized, the distilled water enters the product container to be mixed with the mixed liquid, and is dispersed into the mixed liquid under the magnetic stirring effect; the emulsified diesel fuel is formed. The method for preparing the micro-emulsified diesel fuel has the advantages that the operation is simple; the atomizing particle size is controllable; the usage amount of functional emulsifiers is low.