A numerical simulation was carried out to investigate the process of gas-liquid reaction in a jet-type singlet oxygen generator by using volume-of-fluid coupled with large eddy simulation. The coupled hydrodynamic and reaction simulations provide detailed information about the reacting flow. Results reveal that the reaction aggravates the jet instability and affects the jet structure significantly due to the differential pressure around the liquid jet. The effects of gas velocity on chlorine conversion and the yield of singlet oxygen were investigated. The key is the increasing of the interface area rather than the convection. This numerical simulation study is convenient for the design of singlet oxygen reactors and the research of gas-liquid two-phase flow with reaction.