In 1989, Qing-Yun Chen’s research group at the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences reported the development of methyl fluorosulfonyldifluoroacetate (FSO₂CF₂CO₂Me or MFSDA) as trifluoromethylation reagent. This reagent is now known as Chen’s reagent, which is perhaps the first well-recognized and widely used trifluoromethylation reagent originate from China. Despite the widespread use of Chen’s reagent in both academia and industry, the detailed mechanism underlying the conversion of Chen’s reagent into a trifluoromethyl source has remained elusive. In this contribution, we conducted a thorough investigation into the reaction mechanism, employing density functional theory (DFT) calculations. Geometry optimizations and frequency analyses were performed using the PBE0/def2-SVP level of theory. To ensure accurate electronic energy calculations, single-point energy calculations were conducted at the ωB97X-D/def2-TZVPP level of theory. The solvent effects were considered using the solvation model density (SMD) model during both geometry optimizations and single-point energy calculations. Furthermore, Gibbs free energies were corrected with GoodVibes, employing Truhlar et al.’s quasi-harmonic treatment by setting all positive frequencies less than 100 to 100 cm^–1. Concentration corrections were applied from 1 atm to 1 mol/L. Our calculations reveal the detailed mechanism governing the generation of copper(I) trifluoromethyl from Chen’s reagent in the presence of a CuI catalyst. An in-depth understanding of such mechanistic details would be helpful for future development of new reaction and application with Chen’s reagent.