Liau (了) in Yongchun dialect can be used as a verb, complement, aspectual particle (quasi-perfect and perfective particle) or sentence-final particle, with a variety of phonetic forms ([liau^(553)]/ [lɔ^(21)]/ [ɔ^(21)]/ [lɔ^(211)]). Based on the description of the relationship between the above functions and phonetics, we can understand the gradual change of syntax and pragmatics in the grammaticalization of liau (了), which provides new evidence for the related research of le in Mandarin or other dialects, and the commonness and individuality of language evolution.