This study is to cover vowel changes in Old English in which a vowel is inserted, as can be seen in such phenomena as breaking where a back vowel is added, diphthongization caused by back umlaut, and palatal diphthongization. It is unique that only the high vowels including /i/ and /u/ are inserted in the phenomea. This can be described as ~{a} insertion in dependency phonology. It is further suggested that this feature may be observable not just in Old English but throughout the history of the English language and let us make some predictions abut the trend of language change.