Can I use LES to simulate steady combustion problem?

Yes: you need to run the simulation unsteady, but enable Averaging in the Iterate panel to average the fields and get a steady solution.

thanks. With your help, I understand that I can use LES to simulate steady combustion problem. Fluent run unsteady simulation to get the steady results. The problem itself simulated by Fluent LES may be a steady problem and a unsteady problem. The flow must be 3D and incompressible and its density can change.