Abstract: The combustion of sodium droplet contains a pre-ignition phase and an ignition phase, and sodium droplet combustion ratio as a function of falling time was calculated from sodium spray fire code. A power function, an exponential function and a linear function were used for fitting the sodium droplet combustion ratio curve, and good agreements were reached. Parameters including residence time and maximum combustion ratio of sodium droplet were included, which can be calculated by sodium spray fire code or measured from free-falling sodium droplet combustion test. The relation between sodium spray fire and single sodium droplet combustion was deduced. The fitting function of sodium droplet combustion ratio with time was applied to simulate the process of sodium spray fire, including deduction of equations of the burned sodium mass, the unburned sodium mass in suspension, the mass of sodium deposited in the sodium pool, and the sodium spray combustion rate. When the sodium leak rate during the spray fire keeps constant, the mass of unburned sodium in suspension is proportional to the sodium leak rate, and the sodium spray combustion rate is proportional to the sodium leak rate. There is direct correction between the sodium spray combustion rate and the temperature or pressure change of cell as a consequence of the sodium spray fire. The generation rate of sodium aerosol, the convective heat transfer between the flame of spray fire and the surrounding gas, and the radiation heat transfer between the flame and walls were deduced from the sodium spray fire combustion rate. In conclusion, by fitting the sodium droplet combustion ratio with simple functions, the sodium spray fire is treated as a heat source and sodium aerosol source, which makes it possible to simulate the whole combustion process of the sodium spray fire and to calculate the evolution of temperature, pressure and sodium aerosol concentration in the accidental cell. The sodium droplet combustion ratio curve and the sodium spray fire combustion rate curve can be compared with experimental results and then be input data of the sodium spray fire simulation. This method is suitable for the simulation of sodium spray fire in safety analysis.