The invention discloses a synthetic method of cetrorelix. According to the method, a Knorr-2-Cl-Resin resin is used as a starting raw material, and ten different amino acid resins are sequentially connected according to a solid-phase synthesis method to obtain a protected decapeptide resin. Fluorenylmethoxycarbonyl is sequentially removed during synthesis, then an N,N-dimethylformamide solution ofbenzotriazole-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate and N,N-diisopropylethylamine is used as a condensation agent for carrying out a condensation reaction to obtain the protected decapeptide resin, an acetylation reaction is carried out after the condensation reaction, side chain protecting groups are removed, a cetrorelix crude product is obtained after cracking, and the obtainedcetrorelix crude product is purified to obtain a finished product. According to the synthetic method, the Knorr-2-Cl-Resin resin is used as the starting raw material, and PyBoP / DIPEA is used as the condensation reagent, so that the polypeptide sequence is easier to synthesize, and the purity of the prepared cetrorelix crude peptide is relatively high.