The Eighteen Scholars who were under Li Shimin's command is an important literatus society with political tint. Politically, they assisted Li Shimin in shooting for the empire, capturing the crown prince and setting the Zhenguan Era. Besides that, they were also influencing the future empire and queen. They cannot replace by anyone in that time. The main contribution of this thesis is studying the Eighteen Scholars, regarding them as whole, and reviewing their excellent contribution to the politics of the Tang dynasty, to display the Eighteen Scholars' political value comprehensively and objectively.