Abstarct: Simulation of fluid flow and heat transfer in porous media is motivated by many authors due to its applications in engineering. So many authors investigated this problem baxse on different models. In this study, a detailed parametric study of natural convection heat transfer inside a square enclosure which is partially filled with porous laxyer is reported. Generalized equations in modeling flow in porous media have been employed which are coupled with the lattice Boltzmann formulation of the momentum and energy equations. The lattice Boltzmann method (LBM) is used to investigate the effects of the configura-tions and the thickness of the porous laxyer on flow pattern as well as heat transfer fea-tures. At first, the obtained results are validated in three cases. A high accuracy is ob-served by comparing results of the present study to other numerical studies. Then the effect of positions and the thickness of porous laxyer on heat transfer rate for different dimensionless parameters, such as Rayleigh number, Darcy number and porosity of the porous laxyer are studied. It is observed that the degree of penetration of fluid into the porous medium depends strongly on the product of Rayleigh and Darcy numbers. So the convection and conduction heat transfer mechanism is observed for various Reyleigh-Darcy numbers. Additionally, it is interest to note that for different vertical porous laxyer positions, the middle position and for different horizontal porous laxyer positions, the laxyers in which located up or down of the cavity provide optimal heat transfer rate. Moreover, by increasing the thickness of the porous laxyer the average Nusselt number decreases. In addition in the moderate Rayleigh-Darcy number, the critical porous thickness (S/L)cr for various porosity of the porous laxyer also is reported.