A method for producing ultra-low-carbon steel belongs to steel-making technology field. The process route is: molten iron desulfuration preprocess -converter smelting -RH vacuum process -slab continuous casting. The iron desulfuration preprocess applies blowing magnesium granules for desulfuration; the converter smelting terminal carbon content and oxygen activity of molten steel; applying slag dam operation when tapping without deoxidation; the ladle furnace proceeds operation of top slag modification and temperature controlling; RH vacuum processing to control the maximum vacuum; applying Alfor deoxidation when the decarburization is finished, and alloying if the deoxidation is finished and assuring the deep vacuum processing time after the deoxidation; calming the molten steel when thevacuum is finished; applying non-carbon covering agent and non-carbon protection slag in the slab casting process; the continuous casting process uses full protection casting, and the casting processcontrols a reasonable pulling speed according to slab section. The advantages are: the invention resolves problem of nozzle clogging and improves castability of the ultra-low-carbon steel and implements multi-furnace continuous casting, and the components of carbon, phosphorus, sulphur and nitrogen of the completed product conforms smelting request of the ultra-low-carbon steel.