Abstract: Abstract: Natural convection in closed cavity has been received considerable attention due to its widely applications in industry, such as in solar energy collectors design, cooling of electronic instruments, energy saving of building and nuclear reactor design, the study of natural convection mechanism in enclosed cavity is of great practical significance for improving the comprehensive performance of these systems. With the rapid development of science and technology, more and more heat sources and components are located in the same enclosed cavity, which will lead to large number of heat generation. How to arrange the heat source elements is very important to the cooling and reliability of the system by the natural convection heat transfer. Lots of studies have shown that the fins attached to the vertical walls inside the cavity can enhance the heat transfer rate in the cavity. In order to study the effect of the material and space position of heat radiation in enclosed space on the heat transfer characteristics of natural convection, the RNG k-ε model of FLUENT14.5 was adopted to analyze the temperature field, flow field, local Nusselt numbers and the average Nusselt numbers of the vertical wall of the air-filled cavity (left side was hot wall, right side was cold wall and the top side was the heat source) with aspect ratio of 1. The results showed that the heat transfer enhancement of the cavity was strongly dependent on the position and material of the fins attached to the vertical walls. The influence of single fin and double fin on the horizontal velocity near the top of the cavity was weak, and the disturbance to the horizontal velocity field near the bottom of the cavity was intense, and the influence trend was very close. This phenomenon was not consistent with that of without heat source. The effect of fins on the horizontal velocity in the core region of the cavity was quite different: the disturbance of single fin on the lower position of the core region of the cavity was more obvious, while the disturbance of double fins on the upper region was more intense. Different number of fins lead to different distribution characteristics of temperature field in the enclosed cavity by changing the flow field structure. When the adiabatic fin was located at 1/6 height above the bottom of the hot wall, the average heat transfer capacity of the hot wall was the strongest. When the heat conducting fin was located at 1/3 height above the bottom of the hot wall, the average heat transfer capacity of the hot wall was the strongest. The combination of 1/3 height above the bottom of the hot wall and 2/3 height above the bottom of the cold wall made the average heat transfer capacity of the hot wall the strongest. The average Nu number of thermal conductive fins arranged at 1/3 height above the bottom of the hot wall was maximum, which was 34.93 and 9.67% higher than that of adiabatic fin arranged at the same location. The average Nu number of thermal conductive fins arranged at 1/3 height above the bottom of the hot wall and 2/3 above the bottom of the cold wall was maximum, which was 14.3% and higher than that of thermal conductive fins arranged only at 1/3 above the bottom of the hot wall. The study has a certain theoretical significance for improving the natural convection cooling effect of electronic components in industrial and agricultural engineering and optimizing the spatial location of heat dissipation components.