In this study, a one-dimensional spherical diffusion flame model was constructed and validated with experimental results. The experiments were carried out in the NASA-Glenn 2.2-second drop tower in which both diffusion flame radius and temperature field were measured as a function of time. The simulation model is capable of both steady and transient calculations in which different approximations for radiation modelling are evaluated. Test simulation results showed that the statistical narrow-band (SNB) combined with discrete ordinates method (DOM) reproduced the experimental results most accurately. It was found that a steady state spherical diffusion flame is not established within the time duration under study. The results provide detailed information about the interaction between gas radiation and flame extinction under microgravity conditions.