The natural convection with large temperature difference is computed numerically using the Low-Mach-Number approximation with temperature dependent viscosity and thermal conductivity. In this study staggered grid system is used in order to hold down the numerical oscillation. Firstly, steady laminar natural convection above a horizontal heat source is simulated in order to validate the simulation method. The result is in good agreement with the analytical solution. Secondly, two dimentional flow field driven by two parallel heat sources is computed. This boundary condition may be regarded as a model situation of the big fire covering both sides of a wide straight road. At the same time, it is interesting to investigate interactions between two thermal plumes. The numerical results disclosed different flow behavior when the imposed temperature of the heat sources is changed and the rest of the governing system parameters are varied.