The diurnal variation of geoelectric field,as one of the most important components in the electric field is a common feature world widely. In this paper,we used the observation data of 9 geoelectric field stations in Chinese mainland,and applied the method of harmonic wave synthesis and temporal superposition. We then conducted statistical analysis on the basic feature of diurnal variation of geoelectric field in time and spatial domain. The data shows that the diurnal variation of geoelectric field mostly are in the types of "two peaks and one valley" or "two valleys and one peak",and the characteristic is basically same in whole year,even though the amplitude and phase are slightly different. We also analyzed the complexity of the diurnal variation of geoelectric field and the correlation of the electromagnetic activity,electrical structure and tide by using the geomagnetic,geomorphic and electrical structure data. We conclude that diurnal variation of geoelectric field mainly result from space electromagnetic activity and electricity structure of underground medium,and it is also influenced by hydrology,geology,and other factors.