The structure and synthesis of cyromazine-amino labeled with 15N were proposed, according to the literature of synthesis of cyromazine with natural abundance and testing requirements of the internal standard. Cyanuric chloride, as the starting material, reacted with ammonia-15N to form 2,4-diamine-15N2-6-chloro-1,3,5-triazine; then the latter reaction with cyclopropylamine, produced Cyromazine-amino-15N2, the desired product by 2 steps. The utilization of ammonia was significantly improved (from 59.0% to 80.0%) by partial substitution of ammonia with sodium carbonate. The yield of Cyromazine-amino-15N2 was 68.1% based on ammonia-15N. The product was characterized by means of NMR and MS. Its chemical purity was 99.7% and isotopic enrichment of 98.8% 15N. The preparated cyromazine-amino-15N2 was used asinternal standard to detect cyromazine by LC-ESI-MS with a good linear relationgship (R=0.99995) at 0.2~5 mg/kg range. So it could be used as internal standard in the field of food safety testing.