Among a lot of renewable energy devices, the fuel cell is one of promising renewable energy source due to its high energy density, zero emission, and location free. In most practical case, fuel cells are not solely used and coupled with other energy devices through a DC/DC converter due to compensate of its weakness such as slow response from load demanding and low power density. Thus, a developing efficient algorithm and circuit of DC/DC converter have been studied for a decade by many groups. However, these studies are not enough because they does not considered intrinsic properties of main components of PEMFC and batter hybrid system which are fuel cell, a battery, and a DC/DC converter. Thus, it is important not only understand fundamental properties of a DC/DC converter but also relation between fuel cell and a battery because they are connected intimately and the behavior of one component gives unexpected effect to other component. In this study, we studied intrinsic role of a DC/DC converter of power and energy sharing between PEMFC and battery. We modeled three main component which are PEMFC, a battery, and a DC/DC converter of the hybrid system base on their intrinsic properties such as I-V curves of PEMFC and battery and duty ratio of a DC/DC converter. Then, we use graphical and mathematical methode for qualitative and quantitative analysis. From this study, we found that intrinsic properties of three components are strongly connected and a DC/DC converter acts as changing intrinsic properties such as internal resistance of PEMFC and a battery.