AbstractWith the data of the geomagnetic meridian observatories in China, 25 geomagnetic storms in the period of 1997 to 1999 have been analyzed by using three kinds of methods which are the method of Natural Orthogonal Components (NOC), Correlation analysis and Fourier analysis. Three steps have been adopted to decompose the storm‐time variation (Dst) relating to the universal time (UT), the solar daily variation (Sq) and the disturbance‐daily variation (SD) depending on the local solar time (LT). The results indicate that (1) The spatial distribution and the temporal evolution characteristics of equatorial symmetric ring current are reflected clearly by the Dst variation. (2) The amplitude of Sq reaches the maximum or the minimum during most main phases in MZL, BMT and QGZ observatories, reflecting the variation of the geomagnetic field with the movement of the Sq focus on latitude. (3) During the main phase, the amplitude of SD reaches the maximum, decreasing slowly in the recovery phase. (4) Correlation analysis and Fourier analyses are effective techniques to extract the variations of Sq and SD.