It is a rule of the phonetic evolution of Putonghua that the whole voiced falling-rising tone changes into the falling tone. However, in the study of the exceptions to the phonetic evolution, it is found that in addition to some of the voiced falling-rising tones still read the falling-rising tone, there are also some cases of the change from the falling tone to the falling -rising tone. But it is different from the phenomenon of the change from the voiced falling-rising tone to the falling tone. In this case of the change from the falling tone to the falling-rising tone, the initial consonant has no clear distinction between voiced and unvoiced. Based on Guang Yun and Dialect Character Form, the researcher lists the common characters in modern Chinese, which read falling tone in the middle ancient ages and the falling-rising tone in Putonghua, and demonstrates the relationship between fallingrising tone and falling tone from the perspectives of dialect, phonogram, variant pronunciation words and rhyme of poetry. The study proves the rationality of the transformation from falling tone to falling-rising tone.