The spectral character of X-ray emitted from laser-irradiated gold disk is studied by using the one-dimensional non-LTE multigroup radiation transport hydrodynamics code RDMG. The applicability of the "three-temperature" model in which the radiation is described with thermal conduction approximation is checked. The simulation results show that the X-ray emitted from the laser-produced gold plasma is in non-LTE, and that the atom model has significant effect on the structure of X-ray spectrum. However, the plasma states, laser absorption efficiency and X-ray conversion efficiency, which are calculated with the "three-temperature" model, are almost the same as those with non-LTE multigroup radiation transport model. This fact indicates that the "three-temperature" model can be used to study plasma states and the energy distributions produced by a laser-irradiated high-Z target. This is meaningful to the 2-D or 3-D simulation.