Abstract: Daily minimum temperature collected at 734 meteorological observation stations in Mainland China are used to identify the first and last frost dates. A frost index is defined to denote various levels of frost using the probability density function and analyze the stability of the first and last frost dates, the characteristics of temporal variations of abnormal first and last frost dates, and the effects of circulation factors on the first and last frost dates. Four major results are obtained. First, with the delay of the first frost date and the advance of the last frost date, the frost-free period has prolonged after the 1990s in the Tibetan Plateau; in addition, frost has disappeared and the frost-free period has prolonged since the 1990s in eastern Sichuan basin and southern China. Second, the stabilities of the first and last frost dates are the best in the 1980s, while the worst stabilities occurred in the 1990s; the area of the maximum stability has increased significantly in response to the changed climate status in the Tibetan Plateau and southern Xinjiang; the stability of the first and last frost dates are the worst in eastern Sichuan basin and southern China, while they are better in other areas; the area of instability has decreased and the region of stability moved northward after the 2000s. Third, the frequency of the abnormal first frost date, last frost date descending order is partial early first frost date, partial late last frost date, special early first frost date and special late last frost date. Furthermore, the frequency of abnormal first and last frost dates is relatively high during the period of climate change and the frequency of abnormally early first frost date is the highest in the 1990s, followed by that in the 1970s and climate change has impacts on abnormal first and last frost date. Fourth, the delay of the first frost date and the advance of the last frost date are closely correlated with the reduced northern hemisphere polar vortex area and the northward shift of the subtropical high; the locations, intensities, and areas of the northern hemisphere polar vortex and subtropical high have an important effect on perennial stability state of the first and last frost dates in the agriculture region of China.