The evolution of vowel i has played a very important role in the historical phonetic evolution of Mongolic language. It has not only transformed itself into other vowels, but also had great impact on the other phonetic evolution. This paper mainly analyzes the changes of vowel i in the non-first syllable in Mongolic language and its phonetic influence on other sounds. In Mongolic language, there are two types of phonetic evolutions caused by vowel i, namely, vowel fronting and consonant palatalization. Vowel i influences the front consonant, and make consonant palatalized, then through palatalization, it affects the front vowels again. With the functional characteristics of vowels transfer to the front consonant or vowel, vowel i itself avianizes and abscises. This kind of relay style phonetic evolutional phenomena is a regular pattern in Mongolic language phonetic evolution. Therefore, consonant palatalization and vowel fronting phenomena are unbalanced in the development of Mongolic languages.