Prepositions in English language have the characteristics of polysemy, and their semantics meanings have significant ab-stract features. Based on the perspective of cognition and taking on and over as examples, this thesis uses the transformation of im-age schema and its metaphorical projection to provide an explanation for the polysemy of prepositions . In-depth exploration of the polysemy of English prepositions aims to further interpret the internal cognitive system generated by specific meanings , and help learners to fully grasp the extension of the meaning of prepositions.