Enoxaparin sodium is a low molecular weight heparin used as an anticoagulant for the prevention and treatment of deep vein thrombosis or pulmonary embolism. Enoxaparin sodium is a white or nearly white powder, tasteless, hypotensive, soluble in water, insoluble in ethanol, acetone and other organic solvents. Aqueous solution has a strong negative charge and can combine with some cations to form molecular complexes. The aqueous solution is stable at pH 7.

　　1. Salt formation. Weigh 30g crude heparin sodium, add purified water to dissolve, get heparin sodium solution; Take 75g benzalkonium chloride, add purified water to dissolve, get benzalkonium chloride solution. Slowly add benzathonium chloride solution to heparin sodium solution, stir while adding, stir evenly and leave for 2 hours. Then centrifuge the centrifuge operation, centrifuge the solid obtained with purified water washing, finally the obtained heparin benzalkonium chloride wet product vacuum drying, to obtain heparin benzalkonium chloride.

　　2. The esterification. 5 times the amount of dichloromethane was added to the obtained heparin benzalammonium chloride. After stirring, benzyl chloride was added to the obtained heparin benzalammonium chloride at 35℃ for 24 hours. At the end of the reaction, 10% sodium acetate methanol solution of 6 times heparin benzalammonium chloride was added, stirred for 10 minutes, stood for 4 hours, and then filtered precipitation. The filtered precipitation was washed twice with methanol to obtain wet crude heparin benzalammonium chloride. Add 8% sodium chloride aqueous solution 3 times the weight of heparin benzyl ester to the crude heparin benzyl ester, stir until completely dissolved, then add methanol 4 times the volume of sodium chloride solution, stir again for 10 minutes, stand for 2 hours, filter, repeat this operation 3 times to obtain the crude heparin benzyl ester. Benzyl heparin was obtained by vacuum drying of benzyl heparin wet product.

　　3. The depolymerization. Purified water 20 times its weight is added to benzyl heparin, stirred to dissolve and heated to 60℃. Dissolve 10% of the weight of heparin benzyl ester sodium hydroxide in pure water, then slowly add to the heparin benzyl ester solution, keep at 60℃, stirring reaction for 2 hours, then adjust the pH value of the solution with appropriate hydrochloric acid to 6.0-6.5, cooling to room temperature, get the depolymerization solution. Add an appropriate amount of sodium chloride to the depolymerization solution, make its concentration 10%, stir until it is completely dissolved, then add methanol 60 times the weight of heparin benzyl ester under agitation, stir evenly, and then leave it for 5 hours to separate the supernatant to obtain enoxaparin sodium wet crude product.

　　4. Oxidation and alcohol precipitation. Add purified water 3 times by weight to the wet enoxaparin sodium crude, stir until completely dissolved, add purified water to bring the solution concentration to 20%. Then add 1% of the volume of sodium chloride solution, stir and heat to 35℃, adjust the pH value of the solution to 9.5-10.0 with sodium hydroxide; Then, 1% of the volume of hydrogen peroxide (30% concentration) was added to the solution at temperature and pH, and the oxidation was carried out for 8 hours to obtain the oxidized solution. The oxidation solution was filtered with a 0.45μm filter element, and the pH was adjusted to 6.0~6.5 with hydrochloric acid. Methanol, 5 times the volume of the filtrate, was added after agitation, and stirred evenly. The supernatant was separated for 5 hours to obtain the oxidized alcohol precipitate of enoxaparin sodium.

　　5. Sterilization and filtration. Add purified water to the oxidized alcohol precipitate at a concentration of 25%, stir until it is completely dissolved, and then filter the solution through the filter element. Sterile filtrate was dried, crushed and mixed with freeze dryer to obtain enoxaparin sodium.