Abstract: This paper reports a theoretical method to calculate the resolved absorption spectra and emission spectra (optically thin) of hot dense plasmas. Due to its fully relativistic treatment incorporated with the quantum defect theory, it calculates the absorption spectra dn emission spectra for single element or multi-element plasmas with little computational efforts. The calculated absoption spectra of LTE gold plasmas agree well with the experimental ones. It also calculated the opticaliy thin emission spectra of LTE gold plasmas, which is helpful to diagnose the plasmas of relevant ICF plasmas. It can also provide the relevant paramenters such as populatin density of various ionic stages, precise radiative propties for ICF studies.