| The North China is in the area of the range 32°N-42°N, 106°E-125°E. It is one of the most important research districts focused on mechanism of strong earthquake. Researchers from domestic and abroad have done many geological and geophysical works in the area and have gotten prosperous results. Most of the researches pay more attention to upper mantle within depth of 100km, while the deeper part was seldom including, especially the part below the lithosphere. Due to the limitation of the study methods, only computerized tomography (CT) in seismology was used to detect velocity structure. Conductivity structure of the subsurface is one of the important physical parameters to reveal the state of the Earth's interior. Mineral conductivity is very sensitive to the Earth's interior temperature, fluid, melt and the existence of volatile as well as their components. How to obtain the conductivity structure in the depth beneath lithosphere is a scientific problem.In order to combine magnetotelluric(MT) sounding data to interpret mantle electrical structure, geomagnetic deep sounding(GDS) of equivalent MT scalar impedance method has been proposed and used in practical research in the last century 90's. Geomagnetic stations distributed in North China recorded valuable data for many years. Using GDS of equivalent MT scalar impedance to the analysis of deep structures is feasible.In this paper, various GDS methods are reviewed and the GDS of equivalent MT scalar impedance method is introduced. This study is based on 15 geomagnetic stations with long-period observation data in North China. We did the data collection, decode and data processing for the data from different instruments, different data types and different times. We obtained the long-period electromagnetic response function of various stations.In the analysis, we chose the continuous and high quality data, applied the GDS of equivalent MT scalar impedance method to obtain the apparent resistivity and phase curves, and analyzed its characteristics; the Rho-plus theory was used to check the consistency between apparent resistivity and the phase and also the rationality of one-dimensional structure; And then, we used OCCAM inversion method, based on the one-dimensional most smooth model , the mantle electrical structure with the depth of 1500km was obtained.Based on the analysis of electrical structure, we can conclude:1. The conductivity increases with depth beneath 100km in North China, which may be related with the increase of the Earth's interior temperature;2. At the junction of the borders of North China and North East China(eg.Dalian, Changli), electrical conductivity was apparently low. Comparing with Tang Ji' research (2003) in the North East China, the gradient of conductivity with depth is much slower. The conductivity of this area is between that of North East China and North China.3. At the western border of North China (eg.Qianling, Tianshui, Yinchuan), the minimum conductivity was noticed. It may be associated with the deep structure and temperature of north-south seismic belt. The conductivity of Qianling station was particularly different: the conductivity gradient with depth is almost the same and the conductivity was significantly lower than that in other regions;4. The eastern part of North China (Jinghai, Zhengzhou, Beijing Ming Tombs) shows high electrical conductivity. It is corresponding to the low seismic velocity structure of the Yanshan-belt according to the study of Zhang Xue-Min, 2006;5. Comparing the electrical conductivity from 410km to 660km in different parts of North China, it was found that the conductivity of the mantle transition zone gradually increased from north to south.
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