The invention relates to a method for reducing the DO (dissolved oxygen) content of steel, which comprises the following steps: I, when the temperature of liquid steel in a converter is greater than or equal to 163 DEG C and the compositions of the liquid steel meet the following conditions: the C content is 0.03 to 0.10 percent, the Si content is less than or equal to 0.02 percent, the Mn content is less than or equal to 0.15 percent, the P content is less than or equal to 0.035 percent, the S content is less than or equal to 0.035 percent and the (O) content is 350 to 850ppm, carrying out steel tapping and simultaneously adding aluminum alloy, silicon alloy, lime and Al2O3-containing slag materials into the discharged steel; II, after the converter tapping is completed, obtaining the liquid steel comprising 0.01 percent of Al, 0.05 to 0.60 percent of Si, and 20 to 45ppm of (O); III, putting a steel ladle into an LF (ladle furnace), and after the slag materials are completely molten, obtaining the liquid steel comprising less than or equal to 0.01 percent of Al and 15 to 35ppm of (O); and IV, after feeding argon into the LF furnace at a speed of 500 to 700Nl/min, stirring the obtained mixture in the LF furnace so as to obtain the liquid steel comprising 5 to 25ppm of (O), wherein the Al2O3 content in the slag is 10 to 30 percent, and the ratio of CaO to SiO2 is greater than or equal to 3.5; and before the steel ladle is taken out from the LF furnace, carrying out bottom argon weak mixing on the steel ladle. The method has the advantages of low production cost, and no water-gap blocked phenomenon happened in the process of continuous casting.