Abstract: In this paper the daily magnetic Ci-indices during the winter-half years of the period of 1956-1959 and 1953-1955 are used to ascertain the magnetic disturbed and the magnetic quiet days.The total number of each kind of the key-days at different periods is around 30.Hence in any month the number of key-days is always less than three.The method of superposed epoch is used to analyze the temperature variations after those key-days at 28 stations in 6ina.The results thus obtained are shown by statistical methods to be useful in the medium-range temperature forecasting in China during the winter-half year.