Various low dc voltage sources and energy storage devices are usually used in the industrial high voltage field. This paper introduces a high step-up pulse width modulation DC-DC converter based on the coupled inductor and resonant capacitor. The converter consists of an input-output in series boost unit and m (m > 1) expandable units, where each expandable unit includes two coupled-inductor-resonant-capacitor units. Meanwhile, due to the existence of resonant unit, all the diodes can realize soft switching.