Abstract: In this paper, a diagnostic method of average ionization degree by X-ray emission spectra of laser-produced gold plasma was presented. The coupled equations between the total intensities of 5f-3d transition arrays of gold M-band and the ion populations were set up based on steady collision-radiative equilibrium approximation, with electron-ion collisional excitation and dielectronic recombination being considered in the populations of exciting states. By the experimentally measured intensities of the 5f-3d transition arrays of gold ions, we deduced the distribution of charge states and average ionization degree of laser-produced gold plasma. Furthermore, we discussed the effects of electron temperature, electron density and dielectronic recombination on the diagnostics, and compared the di