The invention discloses an industrial synthesis method for coumarin and relates to the technical field of organic synthesis. The method comprises the steps of adding salicylaldehyde and potassium carbonate into a reactor, slowly adding acetic anhydride into the reactor from an overhead tank, carrying out a condensation reaction while controlling the reaction temperature to be below 200 DEG C, putting the obtained crude coumarin product into a relay tank, then, transferring the crude coumarin product to a water washing kettle for water washing, then, pumping the crude coumarin product into a rectifying still, condensing the obtained cut, then, feeding the condensed cut to a crystallization kettle, adding ethanol into the crystallization kettle, carrying out crystallizing and centrifuging, rectifying a centrifuging stock solution by a rectifying still so as to recover the ethanol, and drying centrifuging solid, thereby obtaining the refined coumarin product. According to the method, the operation is simple, and intermediate products are not subjected to refining treatment and are directly applied to next-step reactions, so that the loss of intermediate products and production workload are reduced, the volume of wastewater produced is low, the raw materials are cheap and readily available, and the prepared coumarin product is high in purity and can be directly applied to flavorings.