Aiming at the problem that the stability of the flat-top pulsed magnetic field generated by open-loop control of capacitor discharge is difficult to meet the requirements of nuclear magnetic resonance, this paper proposes a closed-loop continuous micro-control scheme for the flat-top magnetic field. A compensation coil is placed in the pulse magnet, which is powered by batteries, adopts the strategy of feedforward control and feedback control, uses the IGBT active region to linearly regulate the magnetic field of the compensation coil, compensates for the fluctuation of the background magnetic field, and forms a highly stable flat-top magnetic field. To this end, this paper designs a driving circuit for IGBTs working in the active region, and builds a prototype for experiments. The results show that the method proposed can increase the magnetic field stability to 50×10^-6, which verifies the feasibility of the scheme.