A two-dimensional (2D) model is developed to analyze the performance and efficiency of H2O/CO2 co-electrolysis in tubular SOEC (solid oxide electrolysis cell). The model fully considers the fluid flow, heat/mass transfer and electrochemical/chemical reactions in the SOEC. The results show that RWGSR (reversed water-gas shift reaction) significantly promotes CO2 conversion ratio. The effect of important operating parameters was comprehensively studied and optimal operating condition was determined. When the inlet gas flows in parallel flow mode with the velocity of 1 m s(-1), TSOEC with the H2O/CO2 molar ratio of 1 at 700 degrees C at 1.4 V achieves the highest efficiency of 59.4% and the syngas conversion ratio of 43.8%. Lowering gas flow velocity decreases the syngas yield but promotes H2O/CO2 convert ratio and efficiency. Finally, calculation found that counter flow is superior to parallel flow. (C) 2014 Elsevier Ltd. All rights reserved.