Cavity receiver plays an important role in the dish solar thermal power system.Its performance can affect the efficiency of the whole system.In the present work,the 2-D-model of six typical cavity receivers are created and FLUENT6.3is used to investigate the approximate estimation of the natural convection heat loss of the cavity receivers.The six typical cavity receivers are calculated at the same aperture diameter(10cm), the same wall temperature(400℃), and the same inclination(α=0°). The result of the present numerical procedure shows that the natural convection heat loss from the spherical cavity receiver is approximately 10% fewer than that of the other five. The effect of AW/A1(inner surface area/aperture area) on the convection heat loss has also been studied for the spherical cavity receiver at different inclinations. The convection heat loss is maximum at 0°(cavity aperture facing sideways) and decreases monotonically with increase in angle up to 90°(cavity aperture facing down). The optimal AW/A1for spherical cavity receiver ranges from 8to 10.