Abstract: By means of discussion of current density distribution theory in semi-infinite and the whole spaee,the conelusion can be reached that current density is smaller when electrode at deeper depth. If the electrode is set at deeper depth,interference of surface noise of artificial and natural electric field can be decreased. Also precision and sensibility of apparent receptivity ps and natural potentla Vsp can be increased. So we can get more Information of earthquake anomaly. Applying the data of more than 6 years at Pinggu station in Beijing,we draw the following conclusion. Many kinds of interference,such as electrieity supply,short circuit caused by lightning stroke, glaeial period and so on can be decreased when deep-well electrode is used. After checking Ninghe Ms 6.9, Ms 6.5, Ms 5.6,and Sanhe Ms 4.8,earthuakes,we can also get that anomaly variation can be prominent when the deep-well electrode is used. Therefore,deep-well electrode observation of natural electric field is a good technique,which is worth spreading.

Key words: Deep-well electrode, Surface electrode, Natural electric field, Earthquake precursory