閩東方言具有特殊的韻變現象，已經有許多研究從共時的角度切入分析韻變現象的變化規律與影響條件。然而，福寧片方言雖然多半沒有明顯而規律的緊鬆韻母隨調共時變化，但透過跨方言點的歷史比較，卻可發現其中福安、周寧與寧德等地，具有韻讀隨調分化的音韻演變，反映了歷時性韻變的跡象。因此，本文同時運用內部構擬與跨方言比較的方法，改從歷時的角度切入探究閩東方言的韻變現象，推論閩東方言的韻母演變同時具有「低化」與「高化」兩種變化趨向：前者主要發生於「高元音」韻腹；後者主要發生於「上升複元音」、「下降複元音」、「三合元音」及「中低元音」等韻腹結構，而且各地發生韻變的聲調條件不盡相同。閩東方言的韻變現象，在南片的福州等地，因相反的變化趨向以及互補的聲調條件，形成具有互補分布的緊鬆韻母系統，共時平面上可分析為單一韻母變化規律；而在北片的寧德等三地，則穩固為歷時性音變，連鎖發生於不同的時間層次，造成多項韻讀的分合演變，反映方言內部韻母系統的結構調整。

In this article, the author simultaneously applies the methods of internal reconstruction and historical comparison to examine the variation of finals in Eastern Min dialects 閩東方言. The conclusions are: 1. There are two tendencies in the variation of finals in Eastern Min: (1) lowering, which occurs with high vowels, and (2) raising, which occurs with ascending diphthongs, descending diphthongs, triphthongs and middle-low vowels. These variations only occur with some specific tones which differ from location to location. 2. The variation of finals affects the Eastern Min of the southern and northern areas differently. In the south, in places such as Fuzhou 福州, it forms a phonetic system with two sets of finals in complementary distribution, one high and tight, the other low and loose; synchronic analysis produces a single rule that can explain the variation of finals. In the north, however, in areas such as Ningde 寧德, the variation causes a string of changes which result in a multiple phonologic evolution of finals. Diachronic analysis and comparison can be used to trace these sound changes.