Abstract: As the trade standard of Trichlorfon-D₆ requires, when determining isotope enrichment of trichlorfon-D₆, sample solution is introduced to ESI-MS by syringe pump, and data are processed by the “Mass Cluster” method to calculate the result. In this study, in order to overcome the time-consuming shortcoming in both sample introduction and data processing progress, liquid chromatography was used instead of syringe pump to introduce sample while a simplified formula was deducted to replace the “mass clusters” during data processing. Then this rapid method is verified, compared to the standard method. When the concentration of sample solution was above 0.1 g/L, isotope enrichment was within ±0.2 atom%D of the corresponding results acquired by the standard method with RSD less than 0.1%. The results showed that this new method was accurate and precise, fully competent of rapid determination and calculation of isotope enrichment of trichlorfon-D₆.