Based on the trajector-landmark pairing and image schema in Langacker’s “cognitive grammar” and Lakoff’s orientational metaphors，the orientational meaning and the projected orientational metaphorical extension of in and on are discussed from the perspective of cognitive linguistics. It is found that the image schema of in is a ‘container’ and is projected onto target domains， namely， time， state， manner and tendency and that of on is a ‘surface’ and is projected onto target domains， such as time， dependence， “a member of…” and state. It helps facilitate vocabulary acquisition analyzing the orientational extension meaning and the cognitive process of such prepositions in English.