This paper uses the method of calculating phonological information to conduct a comparative study of the sound, rhyme, and tone of the Middle Chinese dialect with those of the Dunhuang dialect, and explores the main evolution trend of the Dunhuang dialect phonological system. The evolution of consonants is as follows: the voiced consonants are devoiced; The differentiation of lip sounds leads to the production of labiodental sounds [f]; The three groups of “Zhi, Zhuang, Zhang” differentiate and combine to produce retroflex consonants [tʂ], [tʂʰ] and [ʂ]; The three groups of differentiation and combination of “jing, jian, xiao” flow out of [ʨ], [ʨʰ] and [ɕ]; The number of zero consonants has increased significantly. The evolution of vowels is as follows: the stop consonant finals [p], [t] and [k] have disappeared; The nasal ending [m] becomes [n]; The nasal ending [n] becomes [ŋ]. The evolution of tones is as follows: the plain tone characters with clear consonants are now read as Yinping, and the plain tone characters with voiced consonants are now read as Yangping; The words with the initial tone of the consonants of the whole clear, second clear, and second muddy tones still read the initial tone; The words with a full voiced initial consonant are merged into the present tone and read as the tone; The words with initial consonants and secondary voiced consonants in the tone of the present day mainly read as Yinping; The pronunciation of the words with a fully voiced initial consonant in the entry tone is mainly Yangping.