In this paper, a bipolar solid-state pulsed power source based on gallium arsenide (GaAs) photoconductive semiconductor switch (PCSS) is designed. By studying the reflection coefficients at the structural end of the two-stage pulse forming line (PFL), the wave processes of single-stage positive and negative pulses as well as bipolar pulses are analysed, and the circuit simulation is carried out by using the PSpice tool. The effect of resistive impedance at the input end on pulse trailing is investigated, and the methods of pulse trailing modulation and pulse width modulation are proposed. Based on the vertically structured GaAs PCSS and the two-stage pulse-forming line structure, a resistor-isolated pulse charging experimental platform is constructed, and the optical path time-triggering technique is adopted to regulate the on-time sequence of the photoconductive switch. The experimental results show that the developed bipolar solid-state pulsed power source generator can produce bipolar nanosecond impulse with peak-to-peak values up to 3.26 kV, pulse widths of 5.6 ns, and a repetition frequency of 1 kHz under a bias voltage of 2.5 kV, which verifies the feasibility of generating bipolar nanosecond impulse by combining an avalanche GaAs PCSS with a multilevel wave topology PFL.