The tonal-pattern of Lanzhou dialect is experiencing a change demonstrated in two aspects: a) Yin-ping 阴平 (T1a) has two variants, falling and level, and the former is being replaced by the latter; b) Shang-sheng 上声 (T2) and Qu-sheng 去声 (T3) are merging. We propose that the tonal change of T1a is partially a result of language contact, and the sandhi T1a from initial position of disyllabic combination also plays a role in extending the level tone to the citation T1a, the change of T1a then further triggers the merger of T2 and T3. Yet whether it is the change of sandhi T1a in the initial position or the change of the surface representation of citation T1a, or the merger of T2 and T3, all the directionality of tonal change is in line with the “clockwise tone shift circle” (Zhu et al. 2015; Yang and Xu 2019). We argue that tone changes are mainly due to internal factors. Although there are external stimuli, the path of tone change follows rules. The illustration of the ongoing tonal-pattern change in Lanzhou dialect will shed light on the understanding of the rules.