The high stability flat-top pulsed magnetic field (FTPMF) is strongly needed for some scientific researches such as nuclear magnetic resonance (NMR) and specific heat measurement. The high stability FTPMF Facility based on the battery power supply with a linear bypass circuit had been built at Wuhan National High Magnetic Field Center the in 2018. The linear bypass circuit mainly consists of insulated-gate bipolar transistors (IGBT) operating in the active region and power resistor. The current of bypass circuit can be adjusted by the gate voltage of IGBTs to achieve the continuously regulation of the voltage division ratio between divider resistor and magnet. As a result, the joule effect of the magnet can be offset and the magnet current can maintain stability with feedback control. With two IGBT FZ3600R17KE3-B2 ($1700 each), the FTPMF at 23.370 T for 100 ms with the stability of 64.2 ppm had been achieved. However, the terminal voltage of the IGBT in this facility is high due to operate in the active region, which limits its through-current capability. With the magnetic strength increase the through-current capability of IGBT will decrease, which means the more IGBTs are needed. In this paper, a current injection equipment is proposed to reduce the terminal voltage of the IGBTs by injecting current to the power resistor. In this way, the through-current capability of IGBT will be enhanced greatly and the regulation scope of the FTPMF system will be expanded with the same number of IGBT.