Abstract: This paper investigated the rates of diesel conversion and reforming over Ni-Yb/γ-Al₂O₃ catalyst (Ni 16%, Yb 5%) in low/high temperature diesel steam reforming with different inlet gases (CO₂, H₂ and CH₄) as well as the influences of CO₂ inlet gas on water-gas-shift and CO deep removal, which are the follow-up processes of the hydrogen production flowsheet based on diesel steam reforming for proton exchange membrane fuel cells (PEMFC). CO₂ or H₂ improves diesel conversion (> 95%) in low temperature (from 400 to 500℃) diesel steam reforming, which can let CH₄ instead of diesel to participate high temperature (from 550 to 750℃) steam reforming, so that carbon deposition can be resisted obviously. However H₂ shows depression on the high temperature steam reforming, and CH₄ inlet gas depresses diesel conversion. When the molar ratio of gas to the total carbon of diesel is around 0. 54, CO₂ inlet gas shows the best improvement on diesel conversion; however the CO content increases in the product gas, so the gas-hourlyspace-velocity of CO water-gas-shift should be reduced to reach the required CO removal ratio. There is no obvious influence on the two-stage methanation for CO deep removal.