The invention relates to a preparation method of diester carbonate. The diester carbonate is produced through oxidation and carbonylation reaction of alcohols compound under the condition of the existence of a carbon monoxide, oxygen and liquid phase catalyzing system, wherein, the liquid phase catalyzing system contains a catalyst, at least one cocatalyst and at least one ion liquid consists of a positive ion and a negative ion, and the positive ion of the ion liquid has a nitrogen heterocyclic ring structure. The preparation method of the invention mainly uses the cocatalyst and ion liquid to enhance the activity of the catalyst and to further improve the catalysis efficiency, and has effects of improving reaction rate and increasing yield.