Abstract: In order to study natural convection in HTR-PM reactor cabin, radiation coefficient, radiation model, flow model and near wall treatment were discussed to explore suitable model used for numerical analysis of natural convection in HTR-PM reactor cabin. Using this model, temperature difference of inner and outer wall, ratio of gap and height in annulus, ratio of cooling wall height and height in annulus, ratio of inner and outer wall radius and temperature distribution were analyzed. Correlations were given for some factors. All these will be reference for design and analysis of HTR-PM reactor cabin.