As a fundamental consideration in natural convection, the flow in a vertical slot has been studied by numerical analyses with the finite element method and experimental investigations. This paper presents a simulation of natural convection in a vertical slot using a two dimensional model with the finite volume method. Regardless of very high Ra number (5×10^5), the numerical analysis results agree with the experimental data very well. In addition, this paper clarifies about the accuracy of the prism elements and hexahedra elements, and the semi-steady phenomenon.