This paper describes an interface method to utilize the hybrid system with fuel cell and battery. The hybrid system has unique advantage to manage energy state between high energy system (fuel cell) and high power system (battery) according to various type ofload. First, the hybrid system is completely modelled and simulated by using Simplorer. The models are sufficiently correct by considering many parameters. Interface method is realized by constructing a DC-DC converter, and experimented under various load conditions.