For the demagnetization of medium to large-sized vessels, the demagnetization quality is difficult to guarantee due to the limitations of single demagnetization equipment in terms of coil size and demagnetization power supply. To address this issue, it is now common to use multiple sets of demagnetization power supplies for joint demagnetization. However, when multiple sets of demagnetization power supplies are used for joint demagnetization, electromagnetic coupling exists between the coils, turning the entire demagnetization power supply system into a coupled system with multiple inputs and outputs. At this point, conventional current control methods struggle to ensure the dynamic steady-state performance of the demagnetization current. Therefore, this paper will analyze the coupling characteristics of multi-demagnetization power supply systems and propose an improved BP-PID current decoupling control strategy to provide a reference for the design of control methods when multiple sets of demagnetization power supplies are used for joint demagnetization.