Abstract: A novel input-series output-series high gain Boost converter was proposed in this paper.Operation principle and property of this converter were analyzed.The new topology was composed of two identical high gain subtopologies with input-series and output-series connection.As the Cf1 and Cf2,the new topology not only had high voltage gain,but also automatically evenly could share current without any sensing when the duty cycle was greater than or equal to 0.5.Compared with the traditional two phase interleaved Boost converter,the ripple of the inductor current,the ripple of the input current and the voltage stress of the switches were reduced because of the double-series structure of the new topology.Consequently,the new topology is very suitable for the application （for example,the fuel cell power system） in which it has low input voltage but high output voltage.Finally,the experiment was built to verify the theoretical analysis.