The invention belongs to the field of solid waste reclamation comprehensive utilization and particularly relates to a soil conditioner prepared from sludge and a preparation method thereof. The soil conditioner is prepared from river and lake bottom mud, conditioner, medium sand, agricultural and forestry residues, biological manure and plant ash, wherein the conditioner is 5% to 8% of the mass of the river and lake bottom mud, the medium sand is 5% to 10% of the mass of the river and lake bottom mud, the agricultural and forestry residues are 5% to 10% of the mass of the river and lake bottom mud, the biological manure is 1% to 5% of the mass of the river and lake bottom mud, and the plant ash is 1% to 3% of the mass of the river and lake bottom mud. The soil conditioner prepared from sludge disclosed by the invention achieves resource utilization of sludge, also fully utilizes sludge, tailings or river and lake sand, tailing sand, pipe network sand and agricultural and forestry residues at the same, achieves the purpose of treating waste through waste, avoids solid waste landfill, land occupancy and secondary pollution, reduces engineering cost of land reclamation, landscaping, forest land plant and the like and is beneficial to ecological environment; in addition, the river and lake sand, the tailing sand, the pipe network sand and the agricultural and forestry residues are separated and sorted from pipe network sludge.