To prevent the explosion hazards of hydrogen energy, in this work, the deflagration behaviors of H₂-air mixtures at equivalence ratios from 0.6 to 1.4 under the effects of C₃HF₇ and CO₂ are experimentally investigated. Deflagration pressure and time indexes at ambient pressure and temperature are obtained. The characteristic parameters of chemical kinetics are analyzed according to a detailed mechanism. The results suggest that C₃HF₇ has dual effects of pressure enhancement and suppression with the rising volume ratio in fuel-lean H₂-air mixtures. It is the F-involved reactions that govern the exothermic process, facilitate the comprehensive conversion of crucial free radicals, and augment the exothermicity of the principal reaction, leading to the elevation in peak pressure. Dilution of CO₂ would decrease the heat release rate of the F-involved reactions and reduce the explosion enhancement effect of C₃HF₇. The results of this work are beneficial to the formulation of mitigation measures for hydrogen explosions.