Abstract: The research of magnetic flux expulsion of 1.3 GHz single-cell superconducting cavity has been carried out with a new set of high precision magnetic measuring and compensating system, combining with 2 K vertical test system of IHEP. The magnetic field at the equator of cavity can be measured with the system and compensated to less than 5.0×10⁻⁸ T. The magnetic flux expulsion effect of superconducting cavity under different surface temperature gradient is measured and analyzed. The rf performance of the cavity pinned with magnetic flux is tested, and the sensitivity of superconducting cavity resistance to magnetic flux pinning and the surface resistance of superconducting cavity under different electric field gradients are studied accordingly. The results show that the developed high precision magnetic field measuring and compensating system can meet the research needs of magnetic flux expulsion of superconducting cavity. Higher surface temperature gradient of superconducting cavity is beneficial to the magnetic flux expulsion. The sensitivity of flux pinning resistance increases with the increase of electric field. The research has also laid a foundation for the development of superconducting cavity.