Abstract: The effect of adding Na2O into the CaO-Al2O3 slag on the viscosities and melting points of the slags when w(CaO):w(Al2O3)=1.1 was investigated, and the influence of several different additives on the viscosities of the slags was compared. The results showed that with the increase of the Na2O content, the viscosities of the CaO-Al2O3 slags decrease at first and then increase, and reach the minimum value when mass fraction of Na2O is 4%. The melting points of the slags increase with increasing additive content of Na2O. The addition of Na2O, Li2O and MgO decreases the viscosities of the CaO-Al2O3 slags. The ability to reduce the viscosities of the slags in descending order is Li2O>Na2O>MgO. Considering the influence of Na2O on viscosities and melting points of CaO-Al2O3 slags, the dosage of Na2O in CaO-Al2O3 slags should not exceed 4%.