A wide-voltage-range current-fed resonant DC-DC converter was proposed in order to address the requirement of high efficiency and a wide voltage range in fuel cell vehicle (FCV) power system. A current-fed bridge was used on the primary side, and an asymmetrical active voltage multiplier was used on the secondary side of the transformer. The voltage gain was significantly enhanced by integrating a resonant voltage-boosting mechanism. An extended asymmetrical pulse width modulation (PWM) technique was employed, which regulated the duty cycle while maintaining a constant operating frequency. The soft-switching operating range was considerably expanded compared with conventional symmetrical modulation, effectively minimizing conduction loss caused by hard switching. The converter had multi-mode operation capability, allowing flexible transition between resonant mode under varying input voltage and load condition. Soft-switching was maintained across the entire operating range, achieving high voltage gain, low input current ripple and high efficiency. Then energy conversion utilization was significantly improved, and the stable operation of FCV power system was ensured. A 500 W low-power experimental prototype based on the TMS320F28335 digital controller was developed to validate the performance of the proposed converter. The experimental result confirmed the feasibility and stability of the converter over the full range of input voltage variation, with a full-load efficiency reaching 95%.