In this paper, a technique to approximate a class of passive delay systems by a bond graph model is investigated. This method is designed to preserve the passivity of the initial model. Through interconnections of passive elementary blocks (passivity is stable under interconnections), a finite dimensional passive approximant is constructed. This finite dimensional model, if need be, is reduced thanks to a Krylov-Lanczos process. Finally, a bond graph realization of this reduced-order model is given and an example demonstrates the usefulness of the whole approximation procedure.