The internal and external changes of language are related to the internal evolution mechanism of language (grammaticalization) and the external mechanism affecting language (society is one of them). External factors sometimes become an important stimulating point of language change. social change leads to language change, and language change reflects social change. The proliferation of postpositions（dependent verb used after substantive) in modern Korean is the result of modern language contact. This paper tries to summarize a changing phenomenon in the history of Korean vocabulary, namely the communication between the Korean Peninsula and the west after modern times, which makes Korean solidify a group of functional words “postpositions (dependent verb used after substantive)” corresponding to English prepositions in the process of contacting with English. It is manifested by the increase in the number of such words and the formatting of usage, which we call the phenomenon of “expansion and solidification”. The phenomenon of expansion and solidification at least shows five characteristics: the solidification of category, the three ways of Korean, China and Japan, the correspondence with English prepositions, the asymmetry of grammaticalization degree and the dual-track of internal and external homogeneity. The revelation of this phenomenon has certain significance in terms of Korean lexical history, typology, grammar and sociolinguistics.