This document reviews three types of electromagnetic detecting sensors: magnetic induction coil sensors, magnetic superconducting sensors and magnetic saturating sensors. Because of its energy free, low threshold and noise value, high stability and sensitivity, the magnetic induction sensor is widely used. But its disadvantages are big size and heavy weight. So it is necessary to analysis the equivalent circuit of magenetic sensor, and to give out the formulas of optimization values of ferromagnetic core coil's basic parameters(N, μc and A c ), finally put forward solutions to the miniaturization design on magnetic induction sensors.