Abstract: In order to supress the formation of yellow phase during vitrification, simulated high-level liquid waste(HLLW) with high content of sulfur and sodium were pretreated by adding Ba(NO₃)₂ solution, and then borosilicate glass waste forms were prepared by traditional melting method. The effects of pretreatment on the formation of yellow phase and its phase structure and microstructure were mainly investigated. The sulfur content retained in the glass waste forms before and after pretreatment were compared. The results show that SO^2-₄ ions in the simulated HLLW can be immobilized in BaSO₄. The amount of yellow phase during the vitrification process can be markedly reduced by the pretreatment. For the generated yellow phase before pretreatment, the main constituents are Na₂SO₄ and LiNaSO₄ along with a small amount of CaMoO₄ and Na₂CrMoO₄. After pretreatment, the X-ray diffraction peak intensity of LiNaSO₄ decreases and BaSO₄, BaMoO₄, and BaCrO₄ phases appear. The sulfur content retained in the glass waste form before pretreatment decreases gradually with increasing temperature. The sulfur content retained in the glass waste form after pretreatment remains almost unchanged in the temperature range of 850-1 050 ℃, and decreases gradually with further increasing temperature. The pretreatment is helpful to improve the sulfur retention especially for the higher sulfate-bearing HLLW.