For the purpose of performing a quantitative investigation into the negati ve effect and superpositive (or peak-heightening) effect of IP on horizontal strata, the present paper taking a three-layered section as an example and em ploying "critical resistivity method" and "dilute coefficient method" makes a quite overall and systematic study on the formation condition, scope and intensity of these effects as well as, various factors affecting their existence, and, on such a basis, puts forward some valuable criteria and regularities. In order to demonstrate the objectivity of the IP negative effect and the correct ness of the theoretical analysis, this paper also gives the results of related mo del experimentation.