The invention relates to a method for synthesizing a broad spectrum antibiotic, namely, chloramphenicol. The method comprises the following steps of: synthesizing (1R,2R)-2-nitro-1-(4-chlorophenyl)-1,3-propanediol by using 4-chlorobenzaldehyde and 2-nitroethylalcohol as raw materials in the presence of a chiral catalyst, and performing catalytic hydrogenation to obtain (1R,2R)-2-amino-1-(4-chlorophenyl)-1,3-propanediol; and performing dichloro acetylization and nitro substitution on the intermediate to obtain the chloramphenicol. By the method, the common chiral resolution and aluminum isopropoxide reduction in the industry at present can be avoided, three wastes are reduced, and the raw materials and reagents are cheap and readily available; 4-chlorobenzaldehyde is selected as a raw material, nitro substitution is adopted, and the generation of byproducts in nitration reaction is reduced; moreover, the method comprises a few synthesizing steps, the yield is high, and the method is more suitable for industrial production.