The invention provides a method for improving cleanness of Nb-Ti containing steel. The method comprises the following steps of: smelting in a top-bottom combined blowing converter under the condition of argon gas bottom-blowing in the whole process; adding small-grain limes and fluorite in a steel tapping process; adding slow-release deoxidizing agent to the top of the slag after the steel tapping; carrying out secondary refining onto molten steel; feeding the refined molten steel to a continuous casting process for carrying out full-protection casting. According to the invention, low-nitrogen molten steel is obtained by adopting an argon gas bottom-blowing mode in the whole converter smelting process, calcium treatment and soft blowing are performed after LF (Low Frequency) furnace refining desulfuration and heating up, Nb-Ti alloying is carried out and the alloy melting is promoted by carrying out soft blowing again. Moreover, oxide impurities can be reduced by calcium pre-treatment and a soft-blowing process, the Nb-Ti alloy is promoted to melt by the soft blowing, impurities are removed by RH (Ruhrstahl Heraeus) vacuum refining and degassing, impurities are further removed by carrying out soft blowing after breaking the vacuum, and casting blank segregation can be weakened by continuous casting and low-superheat-degree casting, so that the purpose of controlling the oxide impurities and the nitride impurities in the steel is achieved.