The invention discloses a preparation method for alpha-hydroxy cyclo-pentadecanone. The method comprises the following steps of: adding a defined amount of dry organic solvent and metallic sodium into a dry reaction device which is equipped with a thermometer, a stirrer, a reflux condensing tube and a dropping funnel; increasing the temperature and boiling the solvent under N2 protection, quickly stirring and breaking the metallic sodium into fine particles; heating the reaction system to a certain temperature, and then slowly dropwise adding N,N,N',N'-tetra-alkyl pentadecane diamide dissolved in the dry organic solvent into the reaction device; after completely dropwise adding, keeping the temperature and reacting for a period of time; after the ending of the reaction, dropwise adding a defined amount of absolute ethyl alcohol and removing the remaining metallic sodium; after the metallic sodium is completely decomposed, filtering and removing the undissolved substances; washing the filtrate with water till becoming neutral; and drying the solvent by rotating, thereby acquiring a crude product of alpha-hydroxy cyclo-pentadecanone. According to the invention, the N,N,N',N'-tetra-alkyl pentadecane diamide is taken as a raw material for acyloin condensation, so that the method has the advantages of high product yield, high purity and suitability for industrial production.