In this paper, I critically reviewed ‘the Hypothesis of Accent Shift’ on the issue of diachronic differentiation of the Korean prosodic systems and suggested ‘the Hypothesis of Tonological Values Change(reverse)’. The main contents of this hypothesis are as follows. Until the time when the sound of Sino-Korean characters were formed, all dialects in Korean had a single tonal system close to ‘mal(馬)-low tone, mal(斗)-high tone, and mal(語)-rising tone’. Before the middle of the 15th century, this system was differentiated into “Middlel Korean and Hamgyeong dialect systems” and “Gyeongsang and Yeongdong dialect systems”. due to changes in the Gyeongsang dialect and Gangwon Yeongdong dialect. The main content of this differentiation is that the Gyeongsang and Yeongdong dialects have undergone changes in “mal(馬)-low tone>high tone, mal(斗)-high tone>low tone”