SOEC (Solid oxide electrolysis cell) has great potential to store unstable renewable energy in form of steady chemical energy. For this application, transient behavior in variable working condition is crucial. A 2D (two-dimensional) dynamic model was developed to predict the dynamic response of H2O/CO2 co-electrolysis in TSOEC (tubular solid oxide electrolysis cell). The dynamic model comprehensively considered the macroscopic fluid flow, microscopic diffusion, heat transfer and electrochemical/chemical reactions in the TSOEC. In this paper, the TNV (thermal neutral voltage) of TSOEC was specifically defined and calculated. The time constants of charge/mass/heat transport processes were evaluated. Further, the responses of current, gas concentrations, temperature, efficiency, conversions to electricity/gas flow/temperature step inputs were respectively studied. Through the study, appropriate transient operations were designed to improve efficiency and conversions. (C) 2015 Elsevier Ltd. All rights reserved.