Khitan Language, as being used as an official language in Liao Dynasty during 10th to 12th century in Northern China contains some features of influence of Chinese Language. By studying the Sino-Khitan transcription, features of Sino-Khitan phonology can be found. These features include: Voiced initial consonants had been devoiced into voiceless aspirated for ping tone, voiceless unaspirated for non-ping tone; Chinese labial-dental initials had been differentiated from Chinese bilabial initials; Alveolar affricates does not exist in Khitan language but were borrowed from Chinese. Unaspirated [ts] was represented by new-invented YZ graph, while aspirated [tsʰ] was merged into [s] and represented by the same YZ graph as [s]; Nasal initial [ŋ] and finals with nasal coda [-ŋ] in Khitan language are borrowed from Chinese; Chinese final [ɨ] is a not a native sound in Khitan language and new YZ graph was specificly invented for this acquired sound. It is mostly used to transliterate zi-si (资思)rhyme of Middle Chinese. By comparing Sino-Khitan phonological features with that of Northern Mandarin, it is to be found that the two system share many phonological characteristics. However, Tangut language, which was used in northwestern China and its geographic area is currently belong to Northern Mandarin speaking area, has many different features in some essential perspectives. The relation between the Sino-Khitan and Chinese language is very close which suggests that the development of Khitan language may be one of the important steps of Northern Mandarin development.