Abstract: Magnetic sensors are widely used in many fields. With the rapid development of technology, high temperature superconducting materials have been applied in the important domain of weak magnetic field measurement. To exploit these applications, we have investigated three kinds of magnetic sensors that have already or promise to meet the requirements of femtotesla (fT, 10－15 T) range accuracy, i.e., high-temperature superconducting quantum interference device (SQUID) magnetometers, and superconducting flux-to-field transformers based on giant magneto-resistance (GMR) and giant magneto impedance(GMI) sensors.Their structure, principle of operation,and signal processing circuits are analyzed and compared.