Abstract: Cotton herbicide SIOC0426 (4-bromo-N-(2-chloro-6-(4,6-dimethoxypyrimidin-2-yloxy)benzyl)aniline) was synthesized in kilo-scale from 2-chloro-6-fluorobenzaldehyde via hydrolysis, condensation, reduction and nucleophilic substitution reactions. The purity of the herbicide was determined by HPLC external standard method, and the impurities of the herbicide were elucidated by HPLC-DAD-MS. The four-step yield is above 80%, and the purity of the final product is greater than 98%. The impurities are unreacted intermediate 2-((4-bromophenylamino)methyl)-3-chlorophenol and Smiles rearrangement product of SIOC0426 . The pilot-scale synthetic method with the advantage of mild conditions, high yield, high purity and less wastes is suitable for industrial scale-up.