The stratified air distribution systems, including under-floor air distribution and displacement ventilation, have satisfied performance in indoor air environment and can potentially reduce space cooling load. Simultaneously, many studies have been done on these systems, but few were focused on the application in school buildings, especially for large space buildings, such as the lecture theatre. This paper investigated the application of floor-level air supply displacement ventilation system in a lecture theatre, and had the objective to optimize the indoor air distribution to achieve better thermal comfort for occupants by numerical simulation. The results demonstrated that thermal comfort in the back rows of occupied zone is not desirable, because of the terraced floor and the thermal plume effect. Increasing the supply air velocity can improve the thermal comfort in a certain extent, but can not solve the problem thoroughly, and draft risk will rise by increased supply air velocity.