通过分析中国大陆76 个地磁台站2008年1月1日至2010年12月31日地磁场Z分量日变幅的时空特征，得到结论如下:①在时间上，回归分析和傅里叶分析结果表明，所有台站地磁Z 分量的日变幅均有明显的周期性变化，周期主要有365 天、183 天、122 天、73 天等，其中365 天的周期振幅最大(即年周期)。②空间上，地磁场Z 分量日变幅随纬度整体呈非线性变化，在25°N 附近存在拐点(极大值点)，在15°～25°N，日变幅随纬度的增加而增加，在25°～50°N，Z 的日变幅随纬度的增加而减小。③通过地磁场Z 分量日变幅时空分布与等效电流对比，结果显示地磁场Z 分量日变幅的时空变化特征主要是由等效电流的时空演化决定的。④若粗略地把地磁场Z 分量日变幅最大值所处的纬度视为等效电流的焦点所在的纬度，则焦点所在纬度夏季最高，春秋季次之，冬季最低，逐日焦点变化最大可达10°。

In this paper，the authors analyze the daily ranges of vertical about 76 geomagnetic stations from January 1，2008 to December 31，2010. They use those data to study the spatial and temporal characteristics of Z ranges and the results are summarized as follows: ① In temporal， they adopt the regressive analysis and FFT analysis to analyze the data，the results show that the Z component daily ranges of all stations have an cyclical variation obviously． The computed Fourier spectra of all the data sets have clearly resolved the required periodicities in the data，in the form of distinct peaks at 365-，183-，122-，and 73-day periods． The power spectral of 365-day is the highest in all periods． ② In spatial，the daily ranges show nonlinear variation with latitude in China． The results show there exists a point of inflexion ( maximal value point) nearby about 25°N． The daily ranges of Z rise during 15°～25°N and have a good linear decrease variation along with 25°～50°N． ③ Comparing the variation of Z daily ranges with the Sq current inversion in spatial and temporal，they find that the Sq current system causes the spatial and temporal characteristics of Z ranges． ④ 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，you can see that these latitudes of foci become higher in summer，lowest in winter and highest during Equinoxes，displaying conspicuously monthly and daily variations． For two successive geomagnetic quiet days，the latitudes of foci may vary ten degrees．

中国地震局地球物理研究所中央级公益性科研院所基本科研业务专项项目(DQJB11C10)和中国地震局震情跟踪任务(2010020705)联合资助