The invention relates to a working electrolyte for a high voltage aluminum electrolytic capacitor, a preparation method thereof and application. The solvent in the working electrolyte is composed of amain solvent and an auxiliary solvent, the main solvent at least contains an alcoholic solvent, and the auxiliary solvent is 3-methoxypropionitrile. Through adopting the 3-methoxypropionitrile as theauxiliary solvent and combining the 3-methoxypropionitrile with the alcoholic main solvent, in particular, ethylene glycol for use, the conductivity of the working electrolyte is greatly increased, high sparking voltage can be kept and can reach more than 480 V, and besides, with the excellent low temperature properties, the use temperature range of products can be broadened, and low ESR and losscan improve the ripple current resistance ability of products.