Abstract: Based on the Stark splitting effect of helium line, the electric field strength of the atmospheric-pressure helium plasma inside a capillary was measured. By precisely synchronizing the trigging signals of the pulsed power system and the spectrometer system, the dynamics of the helium plasma inside the capillary during the discharges at the rising edge and falling edge of the voltage pulse were investigated via electric field measurement. It was found that the electric field strength during the discharge at the rising edge of voltage pulse was about 15.1 kV/cm at the position of 15 mm away from the needle tip, which was much higher than the electric field strength during the discharge at the falling edge of voltage pulse. However, the dynamics of the plasma propagation showed that the propagating velocity of the plasma for the discharge at the falling edge of voltage pulse was greater than that for the discharge at the rising edge of the voltage pulse. Detailed analysis revealed that the high seed electron density inside the discharge channel played a significant role in the plasma propagation during the discharge at the falling edge of voltage pulse.