Thai League 3 Play-off Round is last promotion quota of Thai League 2. Thai Football clubs, which is runner-up of 2017 Thai League 3 Upper Region and runner-up of 2017 Thai League 3 Lower Region, pass to 2017 Thai League 3 Play-off Round. This round plays Home-Away match. Thai Football clubs get more total scores when finish Home-Away match to promote Thai League 2. Away goals rule is used to this tournament.