The invention provides an acidic soil improver which comprises the following raw materials in parts by weight: 30-50 parts of steel slag and 100-150 parts of ripe sludge. By combining the steel slag with the alkalinity and nutrient elements with the organic matters in the ripe sludge, the acidic soil improver can improve the soil acidity and lower the heavy metals in the soil. Meanwhile, the acidic soil is usually companied by the phenomenon of lack of organic matters, the ripe sludge has high organic fertilizer component content and stability and the characteristic of long acting time, and thus, the acidic soil improver can loosen the soil, enhance the water retention capacity, promote the continuous improvement on the physicochemical properties of the soil and provide a favorable environment for plant growth.