A slag-based composite modifier(SBCM) was proposed for more effective sludge drying and solidification. The optimum composition of SBCM was determined by Uniform design and corresponding mathematical modeling. Sludge drying experiments were performed and the effectiveness of sludge solidification was examined using Chinese leaching toxicity test. The experimental results showed that optimized-SBCM behaved better than quicklime in sludge semi-drying and the leaching concentrations of heavy metal of SBCM-solidified products were lower than the sudge-quicklime mixture. Besides, microscopic analyses using XRD revealed that the main hydrated product of solidification was ettringite, which played an important role in the effective setting process and immobilizing most heavy metals of sludge. Sewage sludge solidified using SBCM could be used as an effective landfill cover.