Abstract: In order to study the law of layered full space direct current sounding curve,the theoretical basis is provided for the innovative application of layered full space direct current method,and the method of theoretical calculation for DC sounding curve of layered whole space and unified classification method is adopted. The results show that under the full space condition the corresponding curve type of n formation is 2n-1(n>0),and more than half space complex,the curve type of layered half space is only a special case where the formation resistivity above the record point is infinite in a full space,in the presence of high resistance layer,the half space curve tail support asymptote 45 degrees rise in space under the condition of its tail to support asymptote at an angle of 0 degrees,it is found that the low resistivity layer than the detection of the high resistance layer has an obvious superiority under the full space condition. With the nature of full space direct current method,many new methods for detecting underground coal mines have been devel- oped. This paper points out the application direction of the full space direct current resistivity sounding method for de- tecting concealed low hazard geological structures such as low resistivity water cut and water conductivity,and enriches the theory of whole space electrical sounding.