We perform a numerical simulation for steady stably-stratified flow over a two-dimensional backward-facing step with the Froude number of 16/9, the Reynolds number of 800 and the Prandtl number of 1.0 by using a newly developed thermal lattice Bhatnagar-Gross-Krook model. A detailed analysis is presented. Excellent agreement between the present results and other numerical data shows that the lattice Boltzmann method is an efficient simulation method for complex flows.