A novel scheme for realizing dense coding with Greenberger-Home-Zeilinger (GHZ) state in linear optical system is proposed. In this protocol, Alice codes on photon 1 and 2 by linear optical element and sents these photons to Bob. Then Bob performs a joint measurement on photons 1, 2, and 3 with the GHZ basis by employing two quantum nondemolition detectors (QND) and polarizing beam splitter (PBS). Eight GHZ states can be completely discriminated. According to the outcomes of his measurement, Bob can determine what operation Alice applied. Alice only transmits two photons in this process of the quantum dense coding, but Bob can obtain three bits of classical information. The QND devices are generally based on cross-Kerr nonlinearities, and the cross-Kerr nonlinearities are available with electromagnetically induced transparency (EIT).