Abstract: The source discrimination of explosives has important value for the investigation of crime case,especially bombing case.In this paper we report that a new method,i、e、isotopic ratio mass spectrometry,was used for the isotopic ratio determination of TNT (a main component in nitramine explosives)which came from four manufacturers. The primary results show: (1) according to their isotopic ratios ( 13 C and 15 N),the manufacturers of origin can be distinguished each other,(2) the minimum consumable amount of sample was lower than l μg,(3) there were the pararell data in EA and GC inlet modes,(4)the measurement precision fell within ± 0 20‰ for 13 C,and ±0 40～0 50‰ fer 15 N.