Abstract: The effects of influent substrate concentration and hydrogen pressure on bioreductive degradation of para-chloronitrobenzene (p-CNB) by autohydrogenotrophic microorganisms were systematically investigated based on hydrogen-based membrane biofilm reactor. Equivalent electron fluxes of bioreductions of electron acceptors and reduction kinetics in biofilm were also analyzed in this study. The results showed that increasing influent p-CNB concentration enhanced p-CNB and p-CAN flux from 0.014 and 0.011 g/(m²·d) to 0.099 and 0.060 g/(m²·d), respectively, but reduced p-CNB removal percentage from 95.9% to 68.4%. As hydrogen pressure increased, p-CNB and p-CAN flux increased from 0.027 and 0.019 g/(m²·d) to 0.028 and 0.022 g/(m²·d), respectively, and p-CNB removal percentage increased from 93.1% to 95.1%. The three modest increments indicated that influent p-CNB concentration affected removal fluxes and percentages of p-CNB and p-CAN more obviously than hydrogen pressure. The results of equivalent electron fluxes and reduction kinetics analysis showed that p-CNB and p-CAN bioreductions were less sensitive to increased hydrogen pressure, further revealing that decreasing p-CNB concentration improved removal efficiencies of p-CNB and p-CAN by microorganisms more significantly than increasing hydrogen pressure. The degree of influence of hydrogen pressure changes on sulfate reduction and denitrification was higher than p-CNB or p-CAN, which showed that hydrogen competition inhibition will be generated on p-CNB bioreduction when the hydrogen availability was limited.