Abstract: In order to study the effects of wall emissivity on natural convection heat transfer characteristics of an air-filled enclosure with built-in fins, the RNG k-ε model was adopted to numerically analyze the temperature field, the flow field and the Nusselt numbers on the vertical wall of the cavity with aspect ratio of 1. The results show that the thickness of the vertical thermal boundary layer and the vertical velocity boundary layer are both increasing due to the combined effect of the built-in fin and the wall radiation. And the horizontal velocity of the top and bottom regions of the cavity fluctuates to a certain extent. When considering wall radiation, the effect of double fins structure on the local heat transfer capacity of the hot wall is similar to that of the single fin structure. When the inside wall emissivity is set to 0.3, 0.6 and 0.9, respectively, correspondingly, the average Nusselt number on the hot wall of single fin cavity will increase by 39.95%, 88.55% and 144.97% compared with that under the condition of no radiation. Meanwhile, the average Nusselt number on the hot wall of double fins cavity are increased by 41.09%, 87.32% and 141.23% compared with that of no radiation, respectively. For the enclosed cavity of the double-fin structure, high wall emissivity is disadvantageous to the convection heat transfer.