The invention relates to electric-power, electron and electric-energy circuits, aim to provide an isolated soft switching two-diode forward resonant DC / DC (direct-current/direct-current) circuit. The circuit comprises a power source, two switching diodes, two clamping diodes, a high-frequency isolation transformer, a primary winding, a secondary winding, an output rectifier diode and an output filter capacitor, and further comprises an input side inductor, a resonant inductor and a resonant capacitor. The resonant capacitor Cr is connected with the power source in parallel, and the input side inductor is located between the resonant capacitor and the power source. The resonant inductor is connected with the transformer primary winding in series. Load formed by the resonant inductor, the resonant capacitor and the output voltage forms resonant circuits in series. By the isolated soft switching two-diode forward resonant DC / DC circuit, a power switching diode operates while zero voltage switches on and quasi-zero current is in switched off state, voltage at two ends of the power switching diode is reduced, overlap time of current passing through the power switching diode is reduced, and switching consumption of the power switching diode is reduced; energy on parasitic inductors or capacitors can be recovered, and energy converting efficiency is improved; energy consumption on the circuit is reduced, and energy is saved.