Concerning the triad of mind, that is, "memory, understanding and will", Augustine in De Trinitate presents to us three different forms successively, namely, static triad of knowledge, dynamic triad of thought, and the triad towards God. This paper holds that while the triadic structure of mind is regarded as image of God, the relationship between these three triads must be revealed from the perspective of temporality of thought. Only through cogitatio as collecting can the triad of mind become an "extension of mind" in time, and can the individual see himself as an image and then point to the eternal Trinity in a dynamic relational way. This study of psychological trinity both provides a necessary temporal perspective to understand the self and its relation to God, and helps us better comprehend the overall concern of Augustinian philosophy.