A robust scheme was proposed for generating maximally W entangled states of cavity field in atom-cavity-fiber system. The scheme requires that the coupling coefficient between cavity and atom is much smaller than Rabi frequency. The atomic spontaneous emission and fiber modes decay are suppressed efficiently via employing adiabatic evolution along dark states. So it is insensitive to the small fluctuation of some parameters. It is also convenient only by adjusting atom-field couplings appropriately to generate W state deterministically. This system can be considered as an ingredient of the quantum network.