Sodium fire accident which was caused by the leakage of liquid sodium is the design basis accidents of sodium-cooled fast reactor. The column flow is a more realistic form of liquid sodium leakage due to the pipe system insulation structure and lower pressure in the sodium-cooled fast reactor. The leaked liquid sodium would combust in the form of columnar fire in the space and pool fire on the ground at the same time to form a mixed sodium fire in a columnar flow. In this paper, a numerical calculation model is established to simulate mixed sodium combustion in a columnar flow. This model is based on the turbulence model, discrete phase model and finite-rate model in Fluent software, and combined with chemical kinetic of sodium combustion. Several variables like spatial temperature, oxygen concentration and pressure during combustion of mixed sodium fire are calculated, and validated with experimental data collected in previous mixed sodium combustion experiment. Besides, the oxygen concentration and the temperature field are calculated for further study of the experiment. The result shows that the spatial temperature calculated by the code coincides well with the experiment, but the chamber pressure cannot be predicted precisely. The oxygen concentration in the center of the sodium flow would decline rapidly in the early stage, then remains at around 5%, but the oxygen concentration in the distance is relatively high. This study could provide reference for evaluation and prevention measures of sodium fire.