Abstract: Based on industrial tests, the deoxidation and desulfurization capabilities and inclusion control performance of 4 refining slags were studied with gas analysis, composition analysis and SEM examination. The results showed that the effect of slag basicity on deoxidation capability is greater than that of Al2O3 mass fraction. The higher the basicity is, the greater the deoxidation capability of the slag is. The deoxidation capability reaches almost the maximum when the basicity is about 4 (slag 3). For desulphurization, the higher the basicity is, the greater the desulphurization capability of the slag is. The desulphurization capability will be lost when the slag basicity decreases to about 1. 5. The increase of desulphurization capability with basicity of slag becomes slower at basicity above 3. 5. Compared with slag 4, slag 3 can control the calcium aluminate inclusions to certain extent, and it can thus be selected as refining slag for 35CrMo.