To address the cooling problem for compact electronic equipment, numerical simulations were conducted using the SIMPLE algorithm with a QUICK scheme. Natural convection was numerically simulated in a small cavity with one, two, or three heat sources. The temperature field, flow field, and three-dimensional characteristics of the system were studied. The results showed that the number of vortices and the air temperature increased with more heat sources. With lower Rayleigh number, heat transfer was better in a square cavity than in a rectangular one. The average Nusselt number at the top plate was larger with the heat source close to the center rather than close to the boundary. The flow and heat-transfer constraints were satisfied by the simulation. Heat transfer was better with the heat source close to the center rather than close to the boundary. The X=Lx/2 temperature fields were similar to two-dimensional temperature fields, and therefore the three-dimensional model could be replaced by a two-dimensional model.