NOVELTY - A pentadecanolide preparation method involves performing esterification reaction, claisen condensation reaction, hydrolysis decarboxylation reaction, clemmensen reduction and cyclization reaction. 15-hydroxyl pentadecanoic acid is mixed with tetrahydrofuran, followed by stirring, adding dicyclohexylcarbodiimide, 4-dimethyl amino pyridine and 4-dimethyl amino pyridine hydrochloride hydrochloride in a dried reflux reaction container capable of introducing gas. Chloroform is added into the obtained mixture followed by stirring, filtering and drying to obtain pentadecanolide.    USE - Method for preparing pentadecanolide for use in medicines, foods and washing chemical product.    ADVANTAGE - The method enables preparing pentadecanolide with energy conserving effect in an eco-friendly, cost effective and simple manner.    DETAILED DESCRIPTION - A pentadecanolide preparation method involves adding dodecanedioic acid and anhydrous methanol into a dried reflux reactor, followed by stirring and mixing uniformly, and adding concentrated sulfuric acid catalyst, where mass ratio of dodecanedioic acid to anhydrous ethanol to concentrated sulfuric acid is 1 g: 6-7 ml: 0.07-0.09 ml. The obtained mixture is stirred and reflowed at 80-95 degrees C for 12-14 hours, followed by cooling to room temperature and adding water for diluting until separating out crystal. The obtained crystal is filtered to obtain crystal filter residue, and adding water as washing agent in mass ratio of 1 g: 10-15 ml, followed by washing, drying and separately collecting the washing solution and the crystal to obtain dimethyl dodecanedioate. The metal sodium and volume of anhydrous methanol is mixed in a mass ratio of 1 g: 7-13.5 ml, followed by stirring and reflowing at 40-45 degrees C until completely dissolving the metal sodium for forming colourless and transparent thick sodium methoxide liquid and adding gamma butyrolactone into the thick liquid. The obtained mixture is stirred at 40-50 degrees C for 40-60 minutes, and the mixture is added into the obtained dimethyl dodecanedioate, followed by stirring, reflowing at 105-115 degrees C, performing claisen condensation reaction for 2-8 hours and cooling to room temperature. The gamma-butyrolactone, dimethyl dodecanedioate and sodium methoxide in a mass ratio of 1: 0.5-1.1: 0.9-1.3 are added into methanol and sodium hydroxide in mass ratio of 1 g: 3-4 ml, where the mixture is added into the claisen condensation reaction mixture, followed by stirring and reflowing at 70-95 degrees C for performing hydrolysis decarboxylation reaction for 5-12 hours to obtain hydrolysis decarboxylation reaction. The mixture of hydrolysis decarboxylation reaction is mixed with 17% of diluted hydrochloric acid in a mass ratio of 1 g: 0.1-0.2 ml, which is taken into a container, followed by cooling, stirring for 2-6 hours, filtering and separately collecting filtrate and the filter residue after primarily filtering. The filter residue is treated by alkali and dried in reflux reactor by adding ether and n-hexane in mass ratio of 1 g: 7-9 ml: 7-9 ml to the filter residue, followed by stirring at 60-80 degrees C for 20-45 minutes and transferring the mixture after reflowing into a container, sealing, standing and crystallizing for 10-40 hours for filtering and collecting the filtrate and the crystal filter residue under acidification reaction. A mercuric chloride is mixed with 10% of diluted hydrochloric acid in mass ratio of 1 g: 20-30 ml, which is taken into a reactor, followed by stirring for completely dissolving the mercuric chloride, and adding zinc powder into mercuric chloride solution in a mass ratio of 1: 8-12. The obtained mixture is stirred for 5-20 minutes, filtered and the filtrate and the filter residue are collected to obtain amalgam zinc. A 15-hydroxyl-12-carbonyl pentadecanoic acid and concentrated hydrochloric acid are mixed with the amalgam zinc in mass ratio of 1 g: 4-7 ml: 0.73-1.76 g, which is taken into a dried reflux reaction container, followed by stirring, reflowing at constant temperature of 114-125 degrees C and performing clemmensen reaction for 5-6 hours to obtain clemmensen reaction product. The clemmensen reaction product is mixed with sulfur powder in mass ratio of 1: 0.03-0.09, which is taken into a reactor, followed by stirring for 1.5-6 hours, removing mercury metal, heating the mercury metal until boiling, primarily filtering, collecting the primarily filtered filtrate and filter residue, heating continuously and cooling the collected primary filtrate for separating out solid until no solid is separated out. A supernatant is collected from the solid on the lower layer, followed by adding acetone and n-hexane in mass ratio of 1 g: 7-9 ml: 79 ml, stirring for reflowing at 65-85 degrees C for 20-45 minutes. The transferring the reflowed mixture into a container, followed by sealing, standing and cry