Abstract: The temperature variations in crop growth period of the last 90 years at Chang chun Station were analysed by means of power spectrum,wavelets and abrupt change methods.The result shows that there are the VLF oscillation about 3 years,long period about 15 years and 60 years.In Song-Liao Plain,from the early 1920's,to the early 1950's,it was a warm period,from the early 1950's to the end of 1970's,it was a cold period,since the end of 1970's,it is a warm period again.The warm period at present will persistent to about 2010's year.The periodic variation of the temperature was discovered with abrupt change method.The cold or warm periods are the same as the results of the wavelet analysis.In crop growth period the abrupt change were taken place.At present temperatuer has a rising tendency.