A scheme is presented for generating four-photon Greenberger-Horne-Zeilinger (GHZ) states with resonant interaction between a cascade type three-level atom and two bimodal cavities. In the proposed protocol, the quantum information is encoded on Fock states of the cavity fields. Schr?dinger equation of the system is solved and quantum states of interaction system are obtained. The detection of atom can collapse cavity to the desired GHZ state. It is shown that the scheme is simple and the experimental implementation is feasible.