The conventional frequency-controlled LLC resonant converter suffers from wide frequency regulation range and low conversion efficiency, so that it is unsuitable for wide voltage range applications with a wide voltage range. In order to solve these problems, a PWM control strategy of the full-bridge LLC resonant converter is proposed in this paper, which realizes the gain adjustment by adjusting the duty cycle of the switch The switches of two lower arms of the resonant converter are controlled by a fixed frequency, and the switching frequency is equal to the resonant frequency, while the switches of the two upper arms are controlled by PWM to adjust the output voltage. With the method, the frequency variation range of the resonant converter is significantly narrowed. In addition, the switches of primary circuit and the rectifier diodes of secondary circuit could achieve zero voltage switching (ZVS) and zero current switching (ZCS), respectively, which effectively reduces the switching losses of the converter. Finally, the 1.5 kW simulation and experimental prototype with 400 V input voltage, 250~500 V output voltage are established to verify the effectiveness of the proposed PWM control strategy.