The invention discloses an ultra-high voltage leaded capacitor and a preparation method thereof, comprising an aluminum shell, a core pack, a rubber plug, and a lead wire, the lead wire is fixedly connected to the core pack, and the rubber plug is arranged close to the electrode. The end of the core package, the lead wire, the rubber plug and the core package are arranged in the aluminum shell sequentially from top to bottom, the core package includes aluminum foil and electrolytic paper, and the core package The aluminum foil and the electrolytic paper are laminated and wound together, and the core package is also impregnated with an electrolyte, the electrolyte includes a solute, a solvent and an additive, and the weight ratio of the solute is 15% ~25%, the weight ratio of the solvent is 60%~70%, the weight ratio of the additive is 5%~15%, and has the advantages of rated voltage reaching 600V and stable operation.