Aiming at localizing the telemetric capsule for detecting gastrointestinal physiological parameters in vivo accurately, a portable alternating current ( AC ) electromagnetic localization system is designed. To verify the feasibility of the method, the model and construction of the localization system are detailed. And static and dynamic accuracy of the localization system are tested by experiments. Next, we compare the simulating results of the electromagnetic radiation aroused by the localization system with the electromagnetic safety standards of human (ICNIRP guidelines and IEEE standard C95. 1 - 1991).Finally, in terms of the results of the static and dynamic experiments, conclusions are drawn that the accuracy of portable positioning system is high (less than 10 mm)enough to satisfy the localization need of the micro invasive medical devices in vivo, and there is no harm of electromagnetic radiation to human.