A resonant power converter and a current synthesizing method therefor are provided. The resonant power converter includes a switch circuit, a resonant tank, a transformer, a rectifier circuit, and a current synthesizing module. The switch circuit receives an input voltage from an input source, and the rectifier circuit outputs an output voltage to a load. The current synthesizing module includes a sensing circuit, a peak hold circuit, and a calculation unit. The sensing circuit is configured to sense a resonant capacitor voltage on a resonant capacitor of the resonant tank. The peak hold circuit is configured to receive the resonant capacitor voltage and acquires a peak value thereof. The calculation unit is configured to receive the peak value, a switching frequency, the input voltage, the output voltage, and a resonant capacitance of the resonant power converter and generate a synthesized output current accordingly.