Abstract: In order to solve the problem that lots of solidified crust of the refining slag during the production process of the GCr15 bearing steel，which resulted the sharply increase of gas and inclusion content in steel，the microstructure and crystal morphology of the refining slag was investigated by SEM and XRD, and the effect of the different composition on crystal morphology was studied. The results showed that the refining slag contained several crystalline phases，and numerous high-melting phases separated out with the decrease of temperature and wrapped up calcium aluminates or strengthened calcium aluminates，which made the refining slag crusted. The composition was optimized in low-melting phase zone，which prevented the solidified crusts effectively. And the qualified rate of w（N）and w（O） were increased by 7.07% and 6.26% in rolled bar，the qualified rate of non-metallic inclusions was increased by 14.70%，the cleanliness of GCr15 steel was improved.

Key words: bearing steel, refining slag, microstructure, crystal morphology