The superconducting magnet is used to provide magnetic field in a magnetic property measurement system (SQUID-VSM, Quantum Design), since it can provide high magnetic field up to 7 T. Due to the pinned magnetic flux, there is residual magnetic field as the magnetic field is set to be 0 from high field. There appears an error between the reported filed and the real filed. Sometimes, the residual magnetic field can be more than 30 Oe. It is so large that it may provide incorrect experiment data, such as Hc, Mr and inverted hysteresis loops. The effect of residual magnetic field on the soft magnetic material measurements should not be neglected. The residual magnetic field is dependent on initial magnetic field. The experimental data must be corrected by measuring the standard sample. In the paper we investigate the origin and the regular pattern of the residual magnetic field. The effects on the measurement results and the correction method are presented.