Chinese characters assimilated into Koreans have been built on the pronunciation environment of the Korean to the needs of contemporary language preferences. They have been passed through hosts of selection process and then have been formed into the sounds of Modern Sino Korean characters. In this paper, we see the characters of XIE SHE YI DENG & ER DENG(蟹攝 1等·2等)’s vowels, and analyse the formation background of Vowels sounds in Modern SinoKorean character in phonetical points, and also examine the three reasons of the formation background as follows. Those are transformation of pronunciation in China, polyphone in Chinese, and characteristic transformation of pronunciation in Korea. First we analyse six different types in the reason of pronunciation transformation in China. First, Characters of HA·JIA· JIE·TAI·GUAI(哈·佳·皆·泰·쾌韻) in KAI KOU YI DENG & ER DENG (開口1·2等)’s combined pronunciation “ㅐ”; Second, Characters of JIA· TAI(佳·泰) in KAIKOU(開口)’s divided pronunciation ‘ㅖ’ in MING and Qing dynasty. Third, Characters of JIA·JIE·TAI·GUAI(佳·皆·泰·쾌韻) in HE KOU YI DENG & ER DENG(合口 1·2等)’s combined pronunciation “ㅙ”; Fourth, Characters of JIA(佳) in HE KOU(合口)’s ivided pronunciation “ㅘ”; Fifth, Characters of JIE·TAI(皆·泰) in HE KOU(合口)’s reflected pronuncitaion “ㅚ”; Sixth, Characters JIA(佳) and JIE(街) of JIA(佳) in KAI KOU ER DENG(開口二等) with JIAN(見)’s pronunciation “ㅏ”. In the acceptance process of polyphone in Chinese, it had been selected only a few of pronunciations in Korea. In the transformation process of characteristics pronunciation in Korea, we especially analyse the three different types, considering easy of pronunciation of Korean people and language environment of Modern SinoKorean characters situation. First, vowel “ㆎ” changed into “ㅐ”; Second, KAI KOU HUA (開口化) in HE KOU YI DENG(合口1等) of TAI YUN(泰韻) with consonants DUAN·TOU·DING(端透定); Third, Characters in KAI KOU (開口) changed into HE KOU(合口).