Abstract: This paper deals with the study of the spatial distribution of the amplitude of diurnal variation of geomagnetic vertical component in China, based on the data recorded at some Chinese geomagnetic stations, using the method of analysis of solar daily variation of geomagnetic field in local regions. The results show that it is necessary to take into account the longitudinal effect in local regions and that the method used here seems to be appropriate. It also shows that the spatial distribution of amplitudes of diurnal variation of the vertical component displays noticeable seasonal variation, month-to-month and day-to-day. If the latitudes of the maximum amplitudes of variation of the vertical component on geomagnetic quiet days are roughly taken as the latitudes corresponding to the foci of Sq overhead current system, we can see that these latitudes of foci become highest in summer, lowest in winter and medium height in Equinoxes, displaying conspicuously monthly and daily variations. For two successive geomagnetic quiet days the latitudes of foci may vary several degrees.