Abstract: The agreement correspondence and morphological co-variation of the internal components in DP are common linguistic phenomena. Previous studies mainly focused on the agreement between phrasal elements, but ignored the agreement in DP. It is found that the main components of agreement correspondence and morphological co-variance in DP are determiners, modifiers and noun heads, which involve notions such as definiteness, person, number, gender and countability. Based on the phasal properties of DP in the framework of Phase Theory, this paper proposes that the uF on the internal phase heads of DP is the motivation for the agreement between the internal components in DP.