In this paper, a novel single-switch high step-up DC/DC converter based on SEPIC topology is presented. The proposed converter operates in quasi-resonant (QR) mode, which comes with many advantages. There are soft-switching conditions in the operation of this converter. In such a way that the power switch turns on under zero-current-switching condition. Besides, the diodes currents are zero during their switching process ( ZCS). This will greatly reduce switching losses and increase the efficiency of the converter. Also, due to the use of coupling inductance capacity, the converter voltage gain is high compared to the converters provided so far. In addition, the voltage gain of this converter is completely independent of leakage inductance value. The operating principles of this converter is studied in detail. In order to verify the theoretical discussion, the simulation process is performed in Simulink/MATLAB software. The simulation results show the accuracy of the converter specifications, well.