However, some limitations of conventional steam gasification still need to be overcome, such as low-purity hydrogen, low reaction temperature, and high tar content. [5,6] Recently, thermal plasma gasification has been under active development. Plasma could provide extreme high temperature and high reactive species for intensification of gasification, which can decompose more than 90% organic components into syngas and break complex long-chain hydrocarbons down without catalysts. [7] Accordingly, the syngas from plasma gasification contains more hydrogen, less tar, and less contaminants than conventional gasification. [8] Hlína et al. [9] indicated that the concentration of tar in the wood plasma gasification syngas (<10 mg Nm −3) was much lower than that of conventional gasification. Luca et al. [10] theoretically demonstrated that the volume fractions of CO and H 2 in plasma gasification syngas were 8% and 7%, respectively, higher than those in entrained flow gasification syngas. A twostage steam plasma gasification process indicated that molar fractions of hydrogen in the product gases were well over 50% for six different types of biomass. [11] Rutberg et al. [12] reported a novel three-phase, steam-air plasma process of high caloric waste. The torch input power is 52-86 kW, and the molar fractions of H 2 and CO in the syngas are around 60% and 30%, respectively. These studies suggest that plasma gasification is a promising hydrogen production technology. There have been studies highlighting the impact of different operating variables on syngas properties during the plasma gasification. Zhang et al. [13] demonstrated that high-temperature steam had a positive impact on the overall gas yield and the lower heating value (LHV) of syngas. A parameter study based on a simulated PGM (plasma gasification melting) process suggested that plasma power, air feeding rate, and steam feeding rate were positive for energy and exergy efficiency. [14] Favas et al. [15] indicated that low temperatures had a more positive effect on the production of hydrogen, while high air equivalence ratio (ER) was not favorable to hydrogen production. However, integrated analysis of the different parameters cannot provide a complete picture of their effects. The synergy effects of different condition parameters and the internal mechanisms behind them need further investigation. Redundancy analysis (RDA) is a powerful chemometric tool for simultaneously evaluating Recently, thermal plasma gasification has attracted much attention due to hydrogen-rich syngas production. In this research, wood sawdust and high density polyethylene (HDPE) mixtures have been investigated under plasma steam gasification with various HDPE contents (0-100%), at different input plasma powers (16-24 kW) and varying steam flow/carbon flow (S/C) ratios (0.2-1.8). The single-factor analysis indicates that the real H 2 yield at 80 wt% HDPE is 23.99% higher than the theoretically calculated results. This significant improvement in hydrogen yield confirms the synergetic gasif...