The invention belongs to the technical field of in-situ repair of heavy 
metal contaminated soil. Municipal 
sludge is used for preparing 
sludge-based 
charcoal through thermophilic thermolysis. The 
charcoal can be used as a repairing agent for the heavy 
metal contaminated soil. The 
sludge charcoal repairing agent comprises thickened sludge and 
palygorskite. A final black product namely the sludge-based charcoal is produced through the steps of performing biological and physical anhydration on sludge, then mixing the sludge after the biological and physical anhydration with the 
palygorskite, performing feeding into an 
atmosphere furnace, and then performing thermophilic thermolysis. The sludge charcoal is produced from the following components of 5-10% of the 
palygorskite and the balance of thethickened sludge. According to the sludge charcoal disclosed by the invention, the municipal sludge is subjected to decrement and harmless treatment, so that the municipal sludge can enter cycle of material and energy in 
natural environment again, and the difficult problem of treating and disposing the sludge is solved. The sludge charcoal is added to the heavy 
metal contaminated soil, so that heavy metal contaminated substances can be effectively solidified, the purposes of being durable and stable in repairing effect and being free from secondary 
pollution are realized, and the sludge charcoal is an ideal soil heavy 
metal contamination repairing agent with low cost.