The invention relates to a method for curing heavy metal sludge by using steel slag, and belongs to the technical field of industrial soil waste resource utilization. The method comprises the following steps: performing steel slag pretreatment, namely, firstly, crushing steel slag, screening granules less than or equal to 2mm, adding water which is 0.12 times of the mass of the granules, uniformly mixing, sealing in a constant-temperature constant-humidity maintenance box, maintaining for 3 hours at the constant temperature of 70 DEG C, and cooling to the room temperature; curing, namely, firstly, uniformly mixing the following components in percentage by mass: 10-90% of steel slag, 1-80% of heavy metal sludge and 1-20% of cement so as to obtain a dry substrate, adding water which accounts for 8% of the mass of the dry substrate, performing casting molding or vibration pressing molding so as to obtain cured blocks, and maintaining the cured blocks in a natural environment for 3-5 days. By adopting the method, not only is the piling problem of steel slag in the prior art solved, but also the problem of heavy metal sludge curing is solved.