漢語語音史上的o、a 元音韻系演變及其所形成的音韻類型差異，反映在各具特色的《切韻》系韻書韻目分類。如：佳皆夬韻次、歌佳麻關係、陽唐韻次、元魂痕韻次、刪山先仙韻次、寒桓之分、仙宣之分、覃談韻次等，均與o、a 元音韻系的發展演變相關。本文比較漢語方言，並以音韻類型差異、鍊動音變、音變階段之不同解析相關韻書韻次之歧異，進而彰顯《切韻》系韻書韻目異同的音韻史意義，討論他們與上古韻部*o、*a 韻系重建結果的關係。上古*o、*a 韻系重建的內容如下：
*-o，*-ok，*-oŋ ╱ *-io，*-iok，*-ioŋ；
*-a，*-ak，*-aŋ ╱ *-ia，*-iak，*-iaŋ；
*-oi，*-ot，*-on ╱ *-ioi，*-iot，*-ion；
*-ai，*-at，*-an ╱ *-iai，*-iat，*-ian；
*-op，*-om ╱ *-iop，*-iom；
*-ap，*-am ╱ *-iap，*-iam；
*-ou，*-iou ╱ **-ouk，**-iouk> *-ok，*-iok；
*-au，*-iau ╱ **-auk，**-iauk >*-ak，*-iak。

Qieyun rhymes order is the reflex of the similarity in sound, such as Jia (佳) Jie (皆) Guai (夬) , Ge (歌) Jia (佳) Ma (麻) , Yang (陽) Tang (唐) , Yuan (元) Hun (魂) Hen (痕) , Shan (刪) Shan (山) Xian (先) Xian (仙), Han (寒) Huan (桓), Xian (仙) Xuan (宣) , and Tan (覃) Tan (談) , all these rhymes being classified as *o,*a vowel final categories. According to Qieyun rhymes order, and concerning the relationship between the Qieyun language and modern Chinese dialects, the most obvious phonological phenomenon of the Gan (贛) , Hakka (客家) and Jin (晉) dialects compared to the rest of the other dialects is having a low back rounded vowel in Grade I rhyme; likewise, there is also a front low opened vowel in Grade II rhyme. Therefore, based on the literature and dialect colloquial readings, I have reconstructed *o,*a vowel final categories in old Chinese phonology. These finals form the following contrastive patterns:
*-o, *-ok, *-oŋ ╱ *-io, *-iok, *-ioŋ;
*-a, *-ak, *-aŋ ╱ *-ia, *-iak, *-iaŋ;
*-oi, *-ot, *-on ╱ *-ioi, *-iot, *-ion;
*-ai, *-at, *-an ╱ *-iai, *-iat, *-ian;
*-op, *-om ╱ *-iop, *-iom;
*-ap, *-am ╱ *-iap, *-iam;
*-ou, *-iou ╱ **-ouk, **-iouk > *-ok, *-iok;
*-au, *-iau ╱ **-auk, **-iauk > *-ak, *-iak