Abstract: Utilizing the methods of nitrogen oxygen analysis, sample-electrolyzing and spectrum analysis, cleanliness of casting slab of Q235 was surveyed under present process in Chuanwei, and the reason of low cleanliness of molten steel was analyzed, and the smelting process for Q235 was optimized.The results show that utilizing slag washing operation, controlling soft blowing time and strength, and reducing slag amount of ladle, large inclusions and T[O] in steel decreased dramatically, cleanliness of steel was significantly increased.