The importance of DC-DC converters with high voltage gain is increasing in many modern applications of power supplies. This kind of converters play an important role in the main part of energy systems. Renewable energy systems connected to the network, hybrid vehicles, and fuel cell are some examples of energy systems. It is important to atttion a low cost converter with, high efficiency, high power density, and high voltage gain which is very important in the applications of green energy systems. Recently, the research trend in high power applications has been concentrated on interleaved converter. Reduction of the current ripple, improved transient response, better thermal distribution and reliability are some of the benefits of interleaved converters. In order to achieve power density increment, passive components size reduction, and fast dynamic response, switching frequency of interleaved converters are increased. However, at high frequencies, the switching losses increase which leads to efficiency, degradation. Furthermore, due to the presence of more semiconductor elements in interleaved converters, the elimination of switching losses is one of their challenges. To eliminate the switching losses, such methods as lossless snubber circuits, active clamp techniques, ZVT, ZCT and Quasi-resonance circuit are used.In the quasi-resonance technique, soft switching condition is provided with the least number of elements and only by adding an inductor and a capacitor. In this thesis, after investigating the different structures of interleaved converters and soft switching methods, a quasi-resonant converter is presented using soft coupling coupled inductors. To reduce the number of switches, the quasi-resonance method is used and the coupling inductor is used to increase the gain and reduce voltage stress of the elements. Also, to reduce the input current ripple, the inductors are cross coupled with each other, and thus the converter operates without a voltage jump. In the past years, there has been a major research an interleaved converters to provide soft switching conditions, but they have provided these conditions with many additional elements. In the proposed converter, soft switching conditions for all components are provided without adding additional semiconductor elements, and the switches are completely turned off softly by simply adding two small capacitors and changing the switching mode. Keywords :High step-up converters, Interleaved convertrs, Soft switching, Quasi resonant