On August 17, 2023, the largest magnet of the HH70 high-temperature superconducting tokamak device, PF4 (the 4th poloidal field coil), was successfully developed. With a diameter of approximately 3 meters, PF4 is the largest among all 26 magnets of the HH70 tokamak and also the largest high-temperature superconducting tokamak magnet currently in China. The main functions of the PF magnets include driving the plasma current and stabilizing the plasma shape. The six PF magnets, together with eight additional CS (central solenoid) magnets, will provide the poloidal magnetic field for HH70.