The invention relates to stable isotope labeled sudan red I and its synthesis method. The invention makes use of an organic synthesis method which comprises: employing stable isotope labeled benzene as a raw material, conducting nitration reaction so as to generate stable isotope labeled nitrobenzene, which then reacts with a reducing agent so as to obtain stable isotope labeled aniline, which is then subjected to diazotization as well as coupling with naphthol, thus obtaining stable isotope labeled sudan red I. Compared with prior art, the stable isotope labeled sudan red I prepared by the invention has chemical purity up to more than 98% and isotopic abundance over 98% after separation and purification, thus fully satisfying the demand for prohibited dye detection in the food safety field.