The invention relates to a method for improving the cleanness of low-phosphorous interstitial free steel. The method comprises the following steps: (1) adding lime after molten steel enters an LF (ladle furnace), adding fluorite, stirring by blowing argon gas at the bottom of a steel ladle or blowing argon gas at the top of an argon gun, carrying out electrode heating for slag melting, observing whether furnace slag is molten, and stopping heating when the furnace slag is molten; strongly stirring the molten steel by blowing argon gas at the bottom of the steel ladle or blowing argon gas at the top of the argon gun for dephosphorizing; after dephosphorizing, stopping argon gas stirring and carrying out temperature measurement; (2) after the molten steel enters an RH vacuum degassing device for decarbonizing and deoxidation alloying, adding lime through an RH alloy bin; (3) adding the last batch of lime and keeping the net circulation of the molten steel for 4-7 minutes. Compared with the prior art, the method has the benefits as follows: the tapping temperature of a converter and the peroxidation degree of IF (interstitial-free) steel are reduced, the oxidability of slag at the top of the steel ladle is reduced, and the aluminum oxide temperature rise amount in an RH vacuum degassing process is reduced, so that the castability and the cleanness of the molten steel are improved.