This paper discusses the original character sou 溲 in the Chuqu 處衢 sub-dialect of the Wu 吳 dialect by examining synchronic correspondence between character and sound in the aspects of consonants, rhymes and tones, as well as doing necessary diachronic strata analysis of the Chuqu dialect. The author found a diachronic stratum with the same sound of you yu hou 幽魚侯 and made sure the sound of sou in Kaihua 開化, Jiangshan 江山, Guangfeng 廣豐, and Yushan 玉山 matches this diachronic stratum. Because of a close relationship between sou and the Yu 魚 category, the author found another diachronic stratum with the same sound of yu ge han huan 魚歌寒桓 and made sure the sound of sou in Longyou 龍游, Suichang 遂昌, Yunhe 雲和, and Qingyuan 慶元 matches such a diachronic stratum. Finally, with regar to the special sound of the Changshan 常山 dialect, the sound of sou may be an exception of sound variation or a later-rising sound of the Zhi category mouth-closed third level character 止攝合口三等字. In conclusion, the original character of the Chuqu sub-dialect should be 溲 except in Changshan 常山.