This paper presents results obtained from a systemtaic theoretical andexperimental study of foundations for ground water prospecting with IPmethod. It shows the relation of η and S_t responses with varied influentialfactors, formulates a mathematical model describing the discharing secondaryfield of IP, suggests an IPparameter called "degree of deviation" which is ofimportant practical value and, from theoretical and experimental study ofequal-ratio array IPsounding on the finite body and horizontal layel, indica-tes the anomaly law of apparent polarizabijity curves and the differencebetween equal-ratio and Schlumberger array. Tt also puts forward an inversedinterpretation method for the finite body and horizontal layers.