The impurity thiadiazole was separated from cefazolin sodium by chemical method, and the separated thiadiazole was identified using thin layer chromatography(TLC), high performance liquid chromatography(HPLC) and infrared absorption spectroscopy(IR) method;The residue of thiadiazole in cefazolin sodium was detected according to the relative retention time;The content of thiadiazole in cefazolin sodium was calculated through peak area ratio between its area in test solution and cefazolin sodium area in 1.0 % reference solution according to European Pharmacopoeia.The results shown that the separated thiadiazole was residual raw material. The proposed method was suitable for the qualitative and quantitative analysis of the residual thiadiazole in cefazolin sodium.The method has been applied to the determination of thiadiazole in several samples and the results show that the contents comply with security specification(not more than 1.0 %).