Calibration-free laser induced breakdown spectroscopy (CF-LIBS) was employed for the quantitative analysis of slag. Nd∶YAG laser ablation was performed in air. The laser-induced plasma emission was measured by an Echelle spectrometer equipped with an ICCD. The plasma temperature and electron number density were determined from Boltzmann plots and a CaⅠ line width, respectively. The assumption of local thermal equilibrium was validated by the Ne criterion. The concentration of oxides was obtained from the concentration of elements by using stoichiometric relation. The calculated oxide concentrations were compared with those obtained by XRF. The relative errors of major elements were less than 15%. The results indicate that this method can be employed for the analysis of major elements in multi-component complex materials without certified reference.