The superconducting / magnetoresistive (MR) composite magnetic sensor is capable of greatly improving the sensitivity of the MR sensor due to thousands of magnetic field magnifications of the superconducting magnetic amplifier. It is expected to achieve the magnetic field resolution of fT level. Thus, the demands of new weak magnetic detection could be satisfied, such as underwater target detection and biological magnetic field detection. After decades of research, the related works of superconducting / MR composite sensors have made important progress and a series of achievements. In this article, the working principle, highly sensitive, and triaxial research status of the composite magnetic sensors are systematically reviewed and summarized. The magnification of the superconducting magnetic amplifier has exceeded 1 000 experimentally, and the thermal noise at low temperature (4. 2 K) is only 2 fT/ Hz. Furthermore, the next research work is also briefly prospected in view of the existing problems. The related works in this article can provide significant guidance for improving the performance of superconducting / MR composite sensors and promoting its popularization and application.