Buoyancy induced flow is one type of flow that can occur in relation to a wide range of hydrocarbon reservoir, deep circulation of groundwater and flow around buried radioactive waste. The objective of the present study was to study the transient two-dimensional natural convection in a fractured porous medium. A computational fluid dynamics (CFD) simulation was carried out to study the velocity and temperature distribution between the two bases of a horizontal solid slab containing a fluid-filled fracture that crosses the slab. The governing equations include continuity, momentum and energy equations with Boussinesq approximation were solved simultaneously using appropriate boundary conditions. This study was confined to work out for low-Rayleigh-number flows. The simulation results were compared with experimental data to validate the accuracy of the CFD work. The CFD results were in excellent agreement with experimental data from the literature. In addition, the effective parameters such as the aspect-ratio and fracture distribution on natural convection were investigated. The results indicated that increasing the aspect-ratio of fracture caused an increase of the maximum velocity in the fracture and temperature profile in the model was affected by fractures communication. Furthermore, the effect of porous medium with a tilted fracture through it was discussed.