The present invention relates to a method of removing petroleum acid from petroleum distillate oil by a membrane dispersion extraction device. A membrane extraction disperser is used; a solvent system formed by sodium hydroxide aqueous solution and ethanol or isopropanol according to the cubage ratio of 0.25 to 4 ®U 1 is considered as a dispersed phase, and the distillate oil containing the petroleum acid is used as a continuous phase, which are respectively heated up till the reaction temperature of 50 DEG C to 110 DEG C, the distillate oil and ethanol-alkali solvent are led into a membrane device according to the cubage phase ratio of the distillate oil and the solvent of 40 to 4 to 1 and the flux of the dispersed phase of 0.5 to 5L/cm<2> per hour, which ensure that the mol ratio of the quantity of NaOH in the solvent after filtering through the membrance and the quantity of NaOH required for neutralizing the distillate oil acid value is 0.9 to 2.5 to 1; more than 95 percent of the petroleum acid in the crude oil distillate oil is removed instantly; instant oil-solvent phase separation is realized; clean oil obtained by the phase separation contains less than 0.5 percent of water, and the content of metal sodium ion in the clean oil is not increased.