By using the first frost date data of national basic (quasi) station during 1961 to 2014, the characteristics of first frost date in Sanjiang plain from three aspects:long time series trend linear change, multiple periodic change and long time sequence were analyzed. The results show that:(1)The initial frost days in Sanjiang plain area are gradually increasing along the southeast direction, and the average vertical span of the whole region is about five days. The overall early frost date of the various regions of Sanjiang plain is delayed, which may be related to the global warming. (2)The spatial distribution of the diurnal variation tendency of the first frost in the Sanjiang plain in 54 years shows the characteristics of "two peak centers and two valleys centers". The two peak centers refer to Jiamusi and Shuangyashan areas as the high incremental centers, which presents the trend of the beginning of the first frost on the gradual decline in the rate of outward trend. The two valleys centers refer to the low-value centers in which the diurnal variation tendency of the first frost in Fujin and Baoqing areas is decreasing outward. The amplitude of the center of the peak is about 1. 5 d/(10 a). The analysis on the variation cycle of daily average early frost days in nearly 54 years in Sanjiang plain areas by integrated wavelet analysis method and HHT-EEMD method show that the Sanjiang plain had two main scale period:the interannual cycle of 2-5 a and the decadal cycle of about 28 a. (3)The crossing point of mean mutation index of the first frost day appeared in 1969, which is tested by 95% significance level and can be used as the research point of the climatic background field in future.