The invention discloses a narrow composition control method for free-cutting non-quenched and tempered steel comprising sulfur, aluminum and nitrogen. The method comprises the procedures of converter steel making, LF refining and VD vacuum treatment, wherein the converter steel making procedure comprises the steps that 0.5-2.0 kg/t of steel reinforced aluminum, an alloy material, 5-10 kg/t of nitrided ferromanganese, 5-10 kg/t of lime and 5 kg/t of premelted slag are added in sequence during tapping, and 1-3 m/t of Al wires are fed behind a furnace after tapping is completed. Through the method, narrow composition control over the contents of S, Al and N in the free-cutting non-quenched and tempered steel can be achieved, the difference between the upper limit and the lower limit of the content of S can be controlled to be 0.010%, the difference between the upper limit and the lower limit of the content of Al can be controlled to be 0.010%, and the difference between the upper limit and the lower limit of the content of N can be controlled to be 0.0030%. Through the method, the contents of the compositions of sulfur, aluminum and nitrogen can be effectively controlled, thus, the product quality and stability are improved, the reject ratio in the production process is lowered, and the method has the characteristics of being low in cost, high in efficiency and the like.