This article presents efficient synthesis of labeled standard Enrofloxacin-D5，with CD3CD2OD as the common substrate．Iodonation of CD3CD2OD with I2 provided CD3CD2I，which was subsequently used to ethylate Ciprofloxacin to get Enrofloxacin-D5。The yield of Enrofloxacin-D5 was 69.9% based on CD3CD2OD consumed．The product was confirmed by NMR and LC-MS to be target compound．Its chemical purity was 99.0% and isotopic enrichment was 99.6 %．It could be used as internal standard in the field of food safety testing．