A current-input-type parallel resonant DC/DC converter and a method thereof are provided. The converter includes an inverter-circuit for inverting/converting an input DC current into a positive-and-negative alternating square-wave-current, a resonant-network for converting the square-wave-current into a sine-voltage, a transformer for realizing the isolation of the power transmission, a full-wave rectifier-circuit for rectifying the sine-voltage, and an output-filter-circuit for producing a DC output-voltage. The inverter-circuit is connected to both terminals of a primary-winding of the transformer through the resonant-network connected in series with the inverter-circuit, a common-polarity terminal of a first-winding at a secondary side of the transformer and an opposite-polarity terminal of a second-winding at the secondary side of the transformer are respectively connected to an input of the full-wave rectifier-circuit, and an output of the full-wave rectifier-circuit and a center-tap terminal at the secondary side of the transformer are respectively connected to an input of the output-filter-circuit.