Abstract: For problems of traditional boost converter including limited boost ability and high capacitor voltage stress, a boost DC-DC converter was proposed which used two quasi-Z-source networks in cascade. Working process of the converter was analyzed, and expressions of step-up ratio and capacitor voltage stress were derived. Compared with traditional Z-source boost converter, the quasi-Z-source converter can realize larger step-up ratio with small duty cycle, and has lower capacitor voltage stress under the same step-up ratio. The simulation and experimental results verify validity of the theoretical analysis.