In order to alleviate the nozzle clogging phenomenon of 38CrMoAl high aluminium steel and improve the production efficiency of continuous casting. This study combines orthogonal design with Factsage thermodynamic calculation to optimize the proportion of refining slag, and verifies it with actual smelting phase to find the best composition of refining slag. The experimental results show that CaO:65%, SiO2:1%, Al2O3:4%, MgO:4% slag system has the highest sulfur capacity, which is 5.665 E-2. The low melting point ratio range of refining slag is CaO:70%~75%, SiO2:1%~3%, Al2O3:6%~8%, MgO:4%~8%. Comparing the number, average area and particle size of inclusions in steel under different proportion refining slag smelting conditions, and considering comprehensively the melting effect and desulfurization performance of refining slag, the refining effect of refining slag component is the best with CaO=70%, SiO2=1%, Al2O3=6%, MgO=6%, CaF2=5%.