Lattice Boltzmann method was used to study natural convection in an isosceles right-angled triangular cavity filled with water-alumina nanofluids. Effects of Rayleigh number, particle volume fraction, heat source location and other factors on convective heat transfer are discussed, as well as effects of nanofluid models on simulation results. It shows that at low Rayleigh numbers, as the heat source moves upward on the left wall, the heat transfer efficiency gradually increases. At high Rayleigh number (Ra=10⁶), the opposite phenomenon was observed. In a single-phase nanofluid model, simulation results show that the average Nusselt number ratio of the hot wall surface increases approximately linearly with the increase of volume fraction. An improved nanofluid model results show that the average Nusselt number ratio increases with the increase of volume fraction, but the slope of the average Nusselt number ratio decreases gradually. The heat transfer efficiency simulated with the improved model is higher than that of the single-phase model. This is because the improved model considers force between particles and heat transfer, which exists in actual situation.