Abstract: Aiming at the unit division and mapping problem of spectral element method for solving the natural convection heat transfer in irregular regions, a length proportional spectral element method based on Gmsh (Geometry Mesh) is proposed. By coupling with SIMPLE algorithm, the convective heat transfer of the elliptical heat source in the closed cavity is solved. The effects of heat source size, long-short axis ratio and rotation angle on the flow and heat transfer in the cavity are analyzed. The research shows that Gmsh can easily divide the irregular region into appropriate units, and the length scale mapping can map the quadrilateral units of any shape while retaining the high precision of the spectral element method. For an elliptical heat source with a constant perimeter and a size L_T/R_i of 0.8, the surface average Nusselt number Nu is positively correlated with the aspect ratio (AR = 0.25 − 1). When the aspect ratio (AR) is 0.5, Nu is also directly proportional to the rotation angle (0°–90°). When Ra is less than 10⁴, the Nu first decreases and then increases with the increase of the heat source size (0.25–0.75). When Ra exceeds 10⁴, the trend reverses. This research provides a reference for the high-precision numerical simulation of convective heat transfer with embedded heat sources in irregular domains using the spectral element method.