Zr-based metallic-glass matrix composites, which were reinforced by continuous tungsten fibers, were prepared by melinfiltration casting. The interface reaction and diffusion were analyzed by using X-Ray diffraction, SEM and EPMA. The influence of Nbcontent of the matrix alloy on the interface reaction and diffusion was also investigated. The results illustrate that for the Zr55Al10Ni5Cu3matrix composites an interface eutectoid reaction between W fiber and Zr in the liquid phase takes place and a W5Zr3 phase is formed athe interface. The interface moves to the direction of the liquid phase. For the matrix alloy containing Nb, the addition of Nb in the liquidcauses a significant change of interface reaction. Nb in the liquid phase exhibits a preferential adsorption at the surface of the W fiber, thusreduces the adsorption of Zr atom in the liquid phase at the surface of the W fiber. The activity of absorbed Zr at interface is decreasedand depresses the interface eutectoid reaction between W fiber and liquid. In this case the interface is a simple diffusion layer only. At thesame time the diffusion coefficient of Zr in the W is decreased by Nb addition and the interface moves to the direction of W fiber.