Methane and carbon dioxide mixture can be used as the fuel in a proton conducting solid oxide fuel cell (SOFC) for power/syngas co-generation and greenhouse gas reduction. However, carbon deposition and low conversion ratio are potential problems for this technology. Apart from using functional catalytic layer in the SOFC to enhance CH4 dry reforming, adding H2O into the fuel stream could facilitate the CH4 conversion and enhance the co-generation performance of the SOFC. In this work, the effects of adding H2O to the CO2-CH4 fuel on the performance of a tubular proton conducting SOFC are studied numerically. Results show that the CH4 conversion is improved from 0.830 to 0.898 after adding 20% H2O to the anode. Meanwhile, the current density is increased from 2832 A m(-2) to 3064 A m(-2) at 0.7 V. Sensitivity studies indicate that the H-2:CO ratio can be effectively controlled by the amount of H2O addition and the H-2 starvation can be alleviated, especially at high current density conditions. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.