The utility model discloses a preparation device of insulating oil of appointed water content, including main case, first vice case and the vice case that holds of second of holding of holding, mainly hold the case, first vice hold the case and the second is vice all sets up a piston in holding the case, the piston links to each other with the piston control ware, the electromagnetic type motor by machine controller control is settled on the main incasement portion top that holds, and the electromagnetic type motor links to each other with the agitating unit top, firstly vice hold that case and second are vice to be held the case and all be provided with into oil pipe, be used for inputing the insulating oily of different water content, first vice hold the vice bottom that holds the case of case and second respectively the defeated oil pipe through being equipped with the oil transportation valve hold the case and be linked together with leading, be used for controlling jointly the oily input of insulation that pours into the owner into and hold the case through piston and oil transportation valve to reduce the air among the main storage box as far as possible. Can prepare out the insulating oil of water content between P1 and P2 within range to the mode of the general water injection stirring of preparation speed, the natural moisture absorption is faster, and the water content of preparation also is more convenient for controlling.