A joint solution model of variable-mass flow in two-phase region and fluid-solid coupling heat transfer,concerned about the charge process of variable-mass thermodynamic system,is built up and calculated by the finite element method (FEM).The results are basically consistent with relative experimental data.The calculated average heat transfer coefficient reaches 1.7×105 W/(m2.K).When the equal percentage valve is used,the system needs the minimum requirements of valve control,but brings the highest construction cost.With the decrease of initial steam pressure,the heat transfer intensity also weakens but the steam flow increases.With the initial water filling coefficient increasing or the temperature of steam supply decreasing,the amount of accumulative steam flow increases with the growth of steam pressure.When the pressure of steam supply drops,the steam flow gradient increases during the maximum opening period of control valve,and causes the maximum steam flow to increase.