The aim of this paper is an attempt to revalue life and outlook on the linguistic study of Ju, Si-Gyeong, and he was the initiator and leader of the standardization movement of the Korean language and orthography systems. Also His original ideas set out in his various works have not been fully evaluated by his followers. His linguistic theory interested in phonology, morphology and syntax. However, He is most impressive in his scholarly attainments is his creative efforts to set up his own phonological and theories.Ju, Si-Gyeong was the scholar who established a certain theoretical system about the Korean grammar in the earliest period. His linguistic study is related to the concept of linguistic theory or description on the comtemporary Korean grammar, and his theory has still become the subject for examination from various points of view.