An ink-jet printing ink of an electron transport layer and its preparing method are provided. The method of the disclosure adopts an ionic conjugated polyelectrolyte as a solute and alcohol compounds as a solvent. By adjusting the proportion of each component, viscosity and surface tension to obtain an ink-jet printing ink of the electron transport layer. The ink-jet printing ink meets the manufacturing requirements and is able to be produced by ink-jet printing process. Simultaneously, it avoids a mutually soluble phenomenon occurred between the electron transport layer and the adjacent structural layers during the preparation of the OLED, which is favorable for the production of a full-solution OLED device. According to the above method, the disclosure satisfies the manufacturing requirements of the ink-jet printing and realizes the ink-jet printing type of the electron transport layer, and is favorable for the production of a full-solution OLED device.