There are three kinds of functional mutation in Hebei dialect:er-hua, D-variation and Z-variation. All these three mutations play multi-functions with the same pronunciation form. The reason for this phenomenon is that each virtual component or affix has its own characteristics of light tone. It can be said that under the direct promotion of light tone, the initial consonant of each virtual component weakens until it falls off to zero consonant, and the vowel tends to centralize until it weakens to a central vowel. It completes the syneresis with the syllables ahead in the fast flow of speech. The result of the syneresis is that the same pronunciation form must bear various semantic or grammatical functions.