English grammatical phenomenon—simple present tense is used to express future time, has always been not only a research hotspot appealing to many scholars’ engagement, but also a teaching and learning difficulty confusing teachers and students for a long time. This work tries to explore this grammar more deeply and comprehensively from the perspective of Prototype Category Theory, in an attempt to gain further development on the related theoretical researches, as well as to provide guidance for the practical teaching and learning. To be specific, this research considers simple present tense as a typical prototype category, and the future time expressed in simple present tense is the peripheral member of prototype category. Excepting introduction and conclusion, there are three main parts: first, the paper demonstrates that it is acceptable to apply Prototype Category Theory in this research from the theoretical aspect, and then establishes the specific analysis framework; second, the paper elaborates the properties of simple present tense as a prototype category, and analyzes the dynamic change of this prototype category from the diachronic perspective; third, a systematical exploration of the peripheral member ( i.e. the future time expressed in simple present tense) has been conducted in this paper in two aspects: cognitive development and the need of language expression.

现在时；将来时间；原型范畴；边缘成员；认知,present tense; future time; prototype categories; peripheral members; cognition