Abstract: Ground 0cm daily minimum temperature collected at 61 meteorological stations were used to identify the first and last frost dates. Linear trend estimation was used to describe the trends in the first frost date, last frost date and the length of the frost-free period. The Mann-Kendall mutation test, the sliding T-test and the IDW method were used to analyze the mutation year and spatial variations of the first frost date, last frost date and the frost-free period in the Huaihe River Basin. The results showed that: (1) with the speed of 2.15, 2.49, 4.38d·10y?1 (P＜0.01) of the first frost date, the last frost date and the frost-free period, respectively, showing the trends in delaying, advance and extension. The rates of change in the three groups were the most significant in the 1990s, at 16.38, 5.34 and 20.6d·10y-1 (P＜0.01), respectively. (2) The first frost date was spatially late in the south, early in the north, early in the mountain and late in the plain. There were 86.9% of the stations postponing significantly (P＜0.05). The last frost date was early in the southwest, late in northeast, early in the plain and late in the mountain, 83.6% stations showed an early trend with the rate of 3.44-5.92d·10y-1 (P＜0.05). The frost-free period decreased with the increase of latitude and altitude. 93.4% stations passed the 0.05 significant level test, and the extension rate of change was 3.56-7.59d·10y-1 (P＜0.05). (3) The locations of the contour lines of 8 November, 1 April and 220 days were slightly northerly about 1° and 2° than the other climate reference periods and the decadal, with the most obvious trend being around 32°N and 34°N, which corroborated the 2nd conclusion. (4) Mutations of first frost date, last frost date and the frost-free period occurred in 2002, 1995 and 1998, respectively.

Key words: Huaihe River Basin, First frost date, Last frost date, Frost-free period