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• Multiple field parameters investigation of plasm-enhanced CO 2 spliting. • A combination analysis of optical emission spectrum and multiphysics simulation of plasma process. • Trade-off effects of plasma power and gas flow on conversion and energy efficiency. • A reduced plasma chemistry set for CO 2 dissociation. • Dissociation reactions of neutrals and electron impact reactions dominated CO 2 splitting. CO 2 dissociation in DBD plasma was thoroughly studied by combining dissociation experiments, multi-physics coupling simulation and in-situ emission spectroscopy measurements. Evolution of spatial–temporal distributions of key field parameters such as discharge mode, electron density (N e), electron temperature (T e), intermediate concentration and reaction rates were analyzed in depth, to uncover the underlying reaction mechanism. The specific energy input (SEI) had a large impact on CO 2 conversion and energy efficiency, and there was a trade-off between plasma power and gas flow rate. The highest CO 2 conversion was achieved a maximum of 15.5% at SEI = 177 J·cm−3 in this work. Meanwhile, the spectrum shows that there was a large amount of CO 2 +, CO, O, and O 2 in the plasma. In addition, we proposed and validated a reduced CO 2 splitting plasma chemistry set to explore the field parameter and key reactin rates distributions. According to the multiphysics modelling, the discharge gap greatly affected the discharge form of DBD, which will subsequently influence CO 2 splitting. In discharge gap > 1.75 mm formation of discharge channels remarkably decreased, and an over small discharge gap (δ g < 1.25 mm) would restrain the electric field range, causing shorter motion path of charged particles and less free electrons, both of which hindered the conversion of CO 2. A thinner dielectric layer can promote CO 2 conversion, due to the reduction in breakdown field strength and increase of high-energy electrons. Electron impact reactions (e + CO 2 → CO + O−, e− + CO 2 → CO + O + e−), reactions of the excited CO 2 * (CO 2 + CO 2 * → CO 2 + CO + O, CO 2 *+O → CO + O 2) mainly contributed to the CO 2 dissociation. [ABSTRACT FROM AUTHOR]