Using the SIMPLE method the natural convection transfer problem of a circle with an internal slotted circle was numerically simulated under different slotting directions.The natural convection heat transfer characteristics of the slotted circle were analysed under different slotting differents according to the numerical results,which coincide well with the experimental results of an existing literature under the same working conditions.In the same slotting direction,the average equivalent thermal conductivity Keqs increases with the increase of Ra.When Ra is small,Keqs does not change basically with the change of slotting direction.When Ra continues to increase,under a same Ra,with the slotting direction changing from vertical to horizontal,Keqs becomes smaller.When Ra exceeds a critical value,the numerical result of Keqs begins to fluctuate,and the critical value is related to the slotting direction.The natural convection heat transfer of a horizontally slotted round within the circle was studied.It is concluded that with the increase of Ra it is possible to obtain stable solution,periodically oscillating solutions,non periodic oscillation solution and ultimately reach a chaos state.