The Heyang dialect has many distinct phonological features, which make it quite different from its adjacent dialects. The phonological features of the Heyang dialect are systematically studied, and the historical strata are revealed. Diverse historical strata exist in the current system of the Heyang dialect. In the Heyang dialect, there are phonological features which belong to the stratum of the Northwestern dialect during the Tang and Song dynasties. These features include: the Middle Chinese voiced obstruents are all aspitrated; the -ŋ ending is lost in the colloquial readings of Dang (宕) and Geng (梗) rhyme groups; the division III hekou syllables in Zhi (止) and Yu (遇) rhyme groups merge; and the division III and IV hekou finals of Xie (蟹) rhyme group are xiyin. The initials yi (疑) and wei (微) in the Heyang dialect are pronounced the same as they are in the Zhongyuan yinyun. The kaikou contrasted with the hekou finals in Guo (果) rhyme group when they combined with velar and glottal initials, the division I contrasted with division II finals of Xiao (效) rhyme group in the Heyang dialect. Those phonological phenomena belong to the historical stratum of the Zhongyuan yinyun. The Heyang dialect was further compared with the Meixian dialect, a representive of the Hakka dialect group. The two dialects share so many phonological characteristics. The relation between the two dialects is even closer than that between the Heyang dialect and Mandarin, in some essential aspects, which strongly suggests that the Heyang dialect may be rooted from the Zhongyuan dialects during the Tang and Song dynasty.