Abstract: In order to improve the RH treatment efficiency and the molten steel cleanliness,some investigations on decarburization processes,oxygen concentration in molten steel and inclusion removal during RH refining were carried out. The decarburization efficiency can be improved through the measures of appropriately controlling the contents of carbon and oxygen during tapping,rapidly increasing the RH vacuum,increasing the lifting gas amount,forcing the decarburization,prolonging the decarburization time,expanding the snorkel diameter and optimizing the snorkel shape. The carbon content of final products is controlled within 20×10^-6 by controlling the increment. The oxygen content in as-cast slabs and the off-grade cold-rolled products due to inclusions are decreased greatly by the optimization of RH heating technology and the development of silicon deoxidation,magnesium deoxidation and tundish covering modification technology. Through the above measures,reasonable ultra-low carbon steel production and increment controlling techniques have been established.