Abstract: Sound variation causes the external form of dialect words to change greatly. It occurs in the commonly-used words. The basic types include dissimilation, assimilation, erhua (r-ending retroflexion-suffication of a nonsyllabic r to nouns, and some verbs and adjectives, causing a retroflexion of the proceeding vowel), leihua and analogous sound and combined sound. To know its original form is favorable for mastering dialect vocabulary. This paper discusses the type, condition, process and cause of sound variation of commonly-used words of Hexi dialect, which is of great significance for the research of the relation of Chinese sound variation with sound and vocabulary.