The invention relates to a preparation method of an embedded capacitor. The preparation method comprises the steps as follows: conductive resin coats one side of each copper foil and is baked to be thoroughly cured; dielectric resin coats conductive resin surfaces and is pre-baked into a semi-cured state; dielectric resin surfaces of two copper foils are oppositely attached, laminated and cured at a high temperature to obtain a double-sided copper-clad laminated plate; the double-sided copper-clad laminated plate is subjected to dry film lamination, exposure, developing, copper layer removal, conductive layer removal and stripping treatment to obtain the embedded capacitor; relatively smooth rolled copper foils or low-profile electrolytic copper foils are adopted as the copper foils; the thicknesses of the copper foils are 1/2oz or 1oz; the dielectric resin surfaces are laminated in a rolling or vacuum laminating manner; copper layers are removed through etching; conductive layers are removed through abrasive blasting or laser depth control cutting; and the dielectric resin can coat twice. Through the structure of the embedded capacitor obtained by the preparation method, the mechanical property of each dielectric layer is effectively kept when the condition that the thickness of each dielectric layer is reduced to strength the capacitor density is ensured.