NOVELTY - A synthesis of allopurinol comprises (A) carrying out condensation reaction to triethyl orthoformate, morpholine, acetonitrile, and acetamide; (B) carrying out ring synthesis reaction; (C) preparing allopurinol crude product; and (D) preparing allopurinol. The step (A) comprises reflux heating triethyl orthoformate, morpholine, acetonitrile, and acetamide. The step (C) comprises adding semi-sulfate into reaction tank, stirring, steam heating, raising temperature to 130-145 degrees C, preserving temperature and reacting for 3 hours, finishing reaction to 35-40oC, and obtaining crude allopurinol.    USE - Method for synthesis of allopurinol (claimed).    ADVANTAGE - The method is simple and effectively improves product yield and quality. Energy consumption and environment pollution in reaction process are reduced, especially using purified water to refine allopurinol.    DETAILED DESCRIPTION - Synthesis of allopurinol comprises (A) carrying out condensation reaction to triethyl orthoformate, morpholine, acetonitrile, and acetamide; (B) carrying out ring synthesis reaction; (C) preparing allopurinol crude product; and (D) preparing allopurinol. The step (A) comprises taking triethyl orthoformate, morpholine, acetonitrile, and acetamide into reaction tank according to order, stirring, steam heating, reflux heating, reducing temperature from 112 degrees C to 80 degrees C, and refluxing reacting for 4 hour, and cooling to 35-40 degrees C, centrifuging, drying mother liquor, and obtaining condensate. The step (B) comprises adding purified water, condensation compound, and hydrazine hydrate into reaction tank according to order, and stirring; raising temperature to 90-102 degrees C, starting timing, performing heat preservation at 90-102 degrees C for more than 30 minutes; reducing temperature to lower than 40 degrees C, adding 10-500 L of dilute sulfuric acid for salifying reaction; performing reaction at 50 degrees C, and salifying until pH value of precise test paper is 1-4; and stopping dripping, continuing to stir for 10-60 minutes, qualifying retest, finishing reaction, reducing temperature to 35-40 degrees C, and obtaining semisulfate. The step (C) comprises adding semi-sulfate into reaction tank, stirring, steam heating, raising temperature to 130-145 degrees C, preserving temperature and reacting for 3 hours, finishing reaction to 35-40oC, and obtaining crude allopurinol. The step (D) comprises adding purified water into feeding tank, stirring and adding crude product, stirring for 5-60 minutes, and pumping by vacuum decoloring tank; adding purified water into carbon tank, adding active carbon, and after stirring for 5-60 minutes, pumping by vacuum decoloring tank; stirring and steam heating, raising temperature to 95-110 degrees C, and performing heat preservation for 30 minutes; and cooling to 25-35 degrees C, centrifuging filter press filtering when it is hot, and drying to obtain final product.