Abstract: A low-frequency field generator based on parallel-line transmission structures is designed for the electromagnetic field radiation immunity test, which can solve the problems of low radiation efficiency, large volume, and difficulty in forming a high electric field strength at low frequencies. A transmission-line balun transformer with 1∶4 impedance transformation ratio is designed to realize the impedance matching between the input port and the load, and the transformation of unbalanced input to balanced output. In order to ensure the stability and reliability of the electrical performances, copper pipes with the diameter 100 mm are adopted as the parallel transmission lines, and non-inductive ceramic resistors are used as the load, which makes the field generator withstand 2500 W continuous waves. The experimental results demonstrate that the field generator has a voltage standing wave ratio (VSWR) less than 1.9 in the frequency band of from 10 kHz–100 MHz. It can generate the electric field up to 200 V/m at a distance of 0.5 meters from the center, and 50 V/m –100 V/m at a distance of 1 m. The electric field generator has the main advantages of high-intensity field strength, wide coverage, uniform distribution, and rotatable polarization.