The invention discloses a method for controlling the sulphur content of molten stainless steel. The method comprises the following preparation steps of (1) molten steel preparing, specifically, a stainless steel material is poured into an electric furnace to be subjected to primary smelting, and molten steel is prepared; (2) AOD furnace smelting, specifically, the molten steel prepared in the step (1) is added into an AOD furnace, first-grade metallurgical lime is added, the basicity of slag is controlled to be 1.5-2.0, and after high chrome-nickel sheet alloy is added into the AOD furnace, blowing oxygen decarburization treatment is conducted; and the carbon content of the molten steel is decarburized to be, by mass, less than 0.03%, ferrosilicon is added to conduct reduction, after sampling and slagging-off are conducted, reducing slag materials are added into the AOD furnace, stirring is conducted, and then steel tapping is conducted; and (3) LF smelting, specifically, the molten steel out of the AOD furnace is hoisted to an LF machining station, dried quartz sand is added so that furnace slag is alkalescent, then the molten steel is fed with CaSi line and added with carbonized rice hulls, and then the molten steel is hoisted out to be poured. Aims at the technical problem that the sulphur content of free-cutting stainless steel in the prior art is difficult to control, the preparation method capable of controlling the sulphur content of the stainless steel precisely is disclosed.