Based on statistics of process data of IF steel （/%： ≤0.0025C, ≤0.005Si, 0.01 -0. 12Mn,≤0. 020P, ≤0. 010S, 0. 02 ～0. 04Als, 0.03 ～0. 05Ti） in steelmaking process, the effect of oxygen content in liquid at Ar station and amount of adding aluminium in RH decarburization period on T[ O] , and the effect of alloys adding procedure, top slag modified treatment and shielding casting process on cleanliness of liquid are analyzed. Research results show that the measures including proper increasing the BOF end oxygen content in liquid and temperature of liquid, extending the interval time between Al and Fe-Ti addition, top slag modifying treating and shielding casting process are available to increase the cleanliness of liquid. It is obtained by commercial production that with the average temperature of liquid at initial RH refining increasing by 2.4 ℃, controlling BOF tapping slag amount to decrease the thickness of top slag layer from original ≥80 mm to 60 ～75 mm as a result during RH decarburization process the adding aluminium heats decreasing by original 36% to 3%, and with top slag modification to decrease the （FeO ＋ MnO） from original 22% to 17% and increase the con- tinuous-continuous casting heats from 8 heats to 10 heats, the T[ O] in liquid in tundish decreases form 37.4 ×10^-6 to 21.6 × 10^ -6 to obviously increase the cleanliness of liquid.