A non-equilibrium thermodynamic model for a steam catapult's steam accumulator is established based on the mass and energy conservation of steam and water by introducing an evaporation (condensation) relaxation time. The accuracy of the model is validated through testing with a lab-based steam accumulator system, which is also used to determine the key coefficients for the mathematical model. The influence of key parameters on the charging performance of the steam accumulator is investigated using potential theory and a mechanism analysis of the non-equilibrium thermodynamic process of the steam accumulator. The results show that the charging time decreases as the charging energy per unit time increases, meanwhile the pressure drop ratio caused by the non-equilibrium thermodynamic process increases as increase of the charging energy per unit time. Furthermore, the main driving force of the macroscopic non-equilibrium thermodynamic process of a steam accumulator is the energy potential difference between the current and the saturated state, increasing the water filling coefficient of the steam accumulator improves its energy storage, but has a negative impact on the cycle time of the system. Finally, the charged steam flow has a stronger influence on the water temperature distribution of the steam catapult's steam accumulator than the steam enthalpy, and plays a leading role when the charging energy per unit time is constant. (C) 2015 Elsevier Ltd. All rights reserved.