Abstract: In Jianchuan dialect, the middle ancient Chinese RI initials are voiceless fricative. Compared to the voiced fricative ?/z
initials in most Chinese dialects, it clearly has evolved toward voicelessness. The internal cause for this evolution is that the devoicing
of the voiced sounds and the isolation and instability of RI initials in the sound system determines the changeability of RI initials. The
essential external cause for the evolution is that Bai people has long been the majority of the ethnic groups in Jianchuan, and there is no
voiced ?/z initials but voiceless s initials in Jianchuan Bai language, which has made the local Chinese phonology align with it.

Key words: Jianchuan dialect, RI initials, voiceless fricative, evolution